noun
gathering spot; hangout; haunt
A place where a particular group of people regularly gather, often with a slightly informal or habitual connotation.
あの公園は近所の子供たちの溜まり場になっている。
That park has become a hangout for the neighborhood kids.
放課後はいつもこのカフェが溜まり場だ。
After school, this café is always our gathering spot.
集合場所 is a neutral, formal term for a designated meeting place, while 溜まり場 implies a habitual, informal gathering spot for a specific group.
Compound of 溜まり (たまり, 'gathering, pooling', nominal form of 溜まる) + 場 (ば, 'place').