The cat is curled up in the corner of the room.
子供たちは公園の隅っこで遊んでいた。
The children were playing in a corner of the park.
Kana spelling is common in casual writing and for learners.
Colloquial diminutive of 隅 (すみ, 'corner'), formed by adding the suffix っこ, which often adds a sense of smallness or endearment.