ish term in computing
(a field well-known for inventing idiotic jargon
instead of using perfectly good terminology
that's been in use often for more than 100 year
A table (in this technical sense) is a geometric arrangement of data, usually and in this case orthogonally in two dimensions:
key | entry1 | entry2 ...
Given a key
value, you may find a row
with that key and read off the entry
or entries. This is called looking it up
Anything else you can do with a table? No, not really. If you really want to get picky, you can also create a new row with a key value. Actually, you probably have to do that in any useful table that's not automatically initialised to the right size.
So why is a table where you look things up known as a lookup table in various parts of computing?
It even has its own abbreviation: LUT. Furrfu!