More general term than "adaptation"
Adjustment = a small alteration or movement made to achieve a desired fit, appearance, or result; the process of adapting or becoming used to a new situation (Google Dictionary).

Adjustment is a very general term; it doesn't mean anything specific in biology or other sciences and it can cover all the terms you've mentioned: adaptation, acclimatization and even learning.

If you check in Thesaurus.com, you can see that synonyms for adjustment include acclimation, acclimatization, modification and improvement, and that one of the synonyms for adaptation is adjustment.