These can only be seen when using the Placidus house system.
An interception means that a specific sign-axis has no house cusps falling into it. You can compare it to a sign floating in a house. Interceptions tend to happen more often in the charts of people that are born closer to the poles on earth.
A Duplication means that a specific sign-axis rules 2 or sometimes even more houses.

Firstly, it’s important to understand what the signs and houses mean in Astrology before moving on.

Meaning of Interception

An unfamiliar or locked energy, a detachment
Areas of life that didn’t get enough attention in childhood
Isolated qualities, hard to reach, weaker awareness
Missing out of a characteristic or life event

There was either an overemphasis or a lack with the interception. An example is a person with a Taurus-Scorpio interception, often times these people were raised in a family that had either a lot of resources, or a family that struggled to make it through the month. In either case the value system is ‘dysfunctional’ for it has not been taught well. This can lead to issues revolving sex, money, trust, low self-esteem,… As a result of the (environmental) circumstances in early life.

The sign show what quality you’re missing in an area (house) of life.

A detachment from the self and the awareness of it. it creates a challenge in dividing the you-me dynamic.
This likely has a root in the childhood as there was no focus onto your own personality development.
This leads to trying to find yourself through others. An issue that can come up is that you project traits of others onto yourself especially when you feel connected to someone. Pretending to be someone else to fill the emptiness is a common trait, however this should be avoided. There can be a possibility that one either puts the focus more onto others or the native may be hyper focused on themselves.
Find who you truly are, find your purpose, your personality and identity.

A detachment from values. A possible root in childhood where there wasn’t much money, a background of a family that didn’t had much resources. Or it could be the other way around too, where a native comes from a rich family. The touch with values is disturbed. The problem that can come up is that one doesn’t have a sense of self worth and value. Self worth can be sought through especially sexual relationships or in merging with people who have the opposite situation of values than yours (poor vs rich), but this doesn’t solve the issue.
Find your own values, create your own resources. Find balance in what you need VS what you feel.

A detachment from your own inner truth and believe system. It can indicate a childhood in a religious family or a non-religious family that didn’t talk about spirituality at all. There is a general emptiness on what the truth is in life, and this often results in feeling lost and confused about the world around. There seems to be a lack in thinking for yourself, projecting other people their believe system onto yourself as you’re seeking the truth. One may change/adjust their beliefs depending on the people they surround themselves with.
Find your truth and faith, within. Believe in what you know yourself, do the research that’s needed.

A detachment from nurturing and stability. You come from a family that is overprotective or you didn’t have a family, either in your feelings or literally such as being an orphan. The absence of one parent is possible. You seek home outside of yourself, in and with other people, but still you feel somehow empty in the end. There is a possibility of following others instead of finding your own path which results in feeling lost, out of touch. There is an issue with grounding and rooting or feeling like you’re a wanderer on this planet without a feeling of home.
Find your roots and root yourself. Find your own ambitions, create your own (sense of) home.

A detachment from what you earn and what your rights are, that what you deserve. This points to an upbringing where you weren’t taught about your own unique self, and that nothing comes easy. There can be confusion or illusions around your own uniqueness. A possibility of following other people their footsteps, not fully acknowledging what belongs to you, in terms of skills, talents, passions or birthrights.. resulting in missing out on what you’re actually good at. There can be issues with the ego in which you can have unrealistic goals for yourself. The ego has not developed properly either leading to no ‘backbone’ or an overemphasis that could make on defensive and high-minded.
Find your own uniqueness and path in life that belongs to you. Find realistic goals that make you happy.

A detachment from how to take care of yourself in a healthy and balanced way. You grew up feeling different from other family members, there can be a feeling that you need to do everything on your own, with a lack of stability in daily routines. There are often struggles around time management, and one may overdo certain activities. You’re either obsessed about your well-being or not at all. it’s an inner struggle between chaos and perfectionism. You likely have difficulty in adapting to change. often it feels like living between two extremes. Either relaxing too much and not getting things done, or addictive behavioral patterns and extreme need for productivity.
Find balance in perfectionism-escapism, full picture VS detail. Build healthy and realistic routines, get rid of bad habits.

Meaning of Duplication

A sign that rules 2 or more houses in the horoscope
A familiar energy & characteristic
An area of life that you’re skilled at and very careful with at the same time

The duplicated sign is where coping mechanisms can be found, as this often functions to ‘make up’ for that lack inside.
However, it also represents a skill, it’s the traits and behavior one has mastered.

You know yourself well. Excellent connection to one’s identity. It can make you act carefully in relationships to others.
You have a tendency to outweigh everything and consider what benefits it can bring to both you as an individual vs the relationship dynamic to another.

You understand values and have an excellent connection to money and your self worth. You’re protective of what you own, with a skill for making and manage finances carefully. Sensuality and sexuality are well developed.

You’re intellectual an very rational. Well developed communication skills and ability to learn/study. You know what words to use and may have a love for literature and knowledge. You find satisfaction in finding truth.

You’re very nurturing and know how to care for others. Very goal oriented and incredibly ambitious. You know how to achieve your goals and have a steady approach to such.

You’re a natural humanitarian. You’re in tune with your dreams and skills. It makes one very passionate and understand the truth about what you earn in life. You’re a genius.

You’re very aware of your well-being. You know how to balance relaxation and hard work. You’re down to earth.
An excellent skill for understanding details.