All chickens are birds but not all birds are chickens?

There must be some word that describes that statement but i can't for the life of me work out what it is and its really bugging me.
Other examples:
All squares are rectangles but not all rectangles are squares.
All iPhones are touch phones but not all touch phones are iPhones.
I could go on, but i'm really keen to know what it is.

Added (1). River, I think you mean causal nexus, not casual. But i mean everyone makes spelling mistakes. Its better than the other answers, but i'm not sure that causal nexus is actually the term that you would use to describe this phenomena.

You are correct

Chickens are a subset of the category of "birds"

I believe this is defined as "Casual Nexus"

The bonding or link between a cause and its effect. The ancient sceptics, subsequent occasionalists, and, most famously, Hume argue that no such link is perceptible or imaginable:

We can see that events do follow one upon another, but we can't see that they must do so, or frame any notion of the necessary connection. The idea that causation is a matter of discrete events joined by links is highly problematic:

What links the event to its link? Is the link to be thought of as a third partner? What is the temporal relationship between the first event, the link, and the later event?"

If you change it up and say "What came first the chicken or the egg?" That is defined as "Causality Dilemma"

To be a rectangle, you need 2 pairs of parallel lines and 4 right angles. A square has 2 pairs of parallel lines and 4 right angles.

To be a square, you need 2 pairs of parallel lines that are equal in length. Not all rectangles have equal lengths for all 4 sides.

So a square can be a rectangle, but a rectangle can't be a square.

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