A colloquial or child-friendly word for snail, often used in everyday speech. The more formal term is カタツムリ.
See also: カタツムリ
On rainy days, lots of snails come out, don't they?
The child is chasing a snail while saying 'maimai, maimai'.
The origin is uncertain, but it may be a reduplicated form related to the verb 舞う (まう, 'to dance'), perhaps from the way a snail's antennae move. The kanji 舞 means 'dance'.