Simple Definition:

Tentative means not definite or final (not certain or decided). It refers to something that is subject to change or is done with hesitation or caution. For example, a tentative plan (a plan that might change) or a tentative answer (an answer given with uncertainty).

Very Simple Definition:

Tentative means not final or certain. It describes something that might change or is done with caution. For example, a plan that might change or an uncertain answer.