An onomatopoeic sound for something being squashed, mashed, or becoming soggy; also used as a short exclamation expressing surprise or disgust.
ケーキを床に落として、ぐちゃになってしまった。
I dropped the cake on the floor and it got all squashed.
子どもが紙をぐちゃぐちゃに丸めて遊んでいる。
The child is crumpling up the paper noisily.
靴が泥でグチャッとなって歩きにくい。
My shoes got all muddy and squelchy, it's hard to walk.