wetland with thick vegetation; marshy thicket
Refers to a swampy or marshy area overgrown with bushes, reeds, or other dense plant life. A somewhat literary or descriptive term.
That bird builds its nest in marshy thickets.
gathering place; place where things collect
Figurative extension: a place where people, things, or information gather, like a hub or hotbed. Rare and somewhat poetic.
This town is a gathering place for artists.
Compound of 藪 (yabu, 'thicket') and 沢 (sawa, 'marsh'). The reading そうたく is an on'yomi-based reading, likely a literary or coined term.