When we think of basic facts, possibly the first thing that springs to mind are our “times tables”. But there is far more to them than this. Just about anything in mathematics can be a basic fact. The main ones encountered are the whole-number basic facts, and in particular addition and multiplication, and their close cousins subtraction and division. However, we should memorise simpler facts, like our addition and subtraction facts. Often these have been ignored. Just maybe 7 × 8 may pop into mind just a tad more automatically than 7 + 8.
Computational estimation is being able to quickly and easily get a number that is close enough to the exact answer of a mathematical problem to be useful. Usually it involves some simplified mental calculation.