Getting a compliment from your effusive Aunt Sally can be a little embarrassing. Since she's so effusive, Aunt Sally holds nothing back, gushing with enthusiasm.
The adjective effusive means "extravagantly demonstrative," and if you know someone who expresses positive emotions in a heartfelt, bubbly way, you understand just what the word means. The word effusive has a surprisingly similar definition in geology; it describes a particular kind of volcanic eruption, one in which lava bubbles up out of the volcano and flows around it.