basic yes, but the point is that we do have binary operations that are not associative.
This is the definition of a monoid.
Monoids are not uncommon, but for sure they are less well known that say a group. An example of a monoid are the real numbers with standard multiplication.
Lie algebras are fundamental in mathematical physics and differential geometry. They are also of great interest from a pure algebra point of view. I would be very suprised if you have not encountered these in your studies - at least just the basics and some simple examples.
Yes, you have defined a monoid. Typically a monoid is a 'group' for which not all the elements have an inverse. So, for the case of the real numbers and muliplication, 0 has no inverse.