To state or express firmly. She asserted her opinion during the meeting.
To behave confidently so that people recognize your presence, value, or authority, especially in the reflexive construction "assert oneself". During the debate she asserted herself and refused to be interrupted.
To exercise or make others recognize (one's rights, authority, or power). The rebels tried to assert control over the northern territory.
In computing, to test a condition in a program and cause execution to halt (or raise an error) if the condition is false. The routine asserts that the buffer length is non-zero before copying data.