This is the 10284th most frequent Russian word.
босиком
Barefoot.
Here the word 'босиком' is used as an adverb indicating the manner of walking without footwear.
Он гуляет босиком по песку.
He walks barefoot on the sand.
In this sentence, 'босиком' is used to describe the state of the subject while experiencing something.
Босиком она чувствовала тепло деревянного пола.
Barefoot, she could feel the warmth of the wooden floor.
In this example, 'босиком' is utilized to set the scene and describe the protagonist's condition upon performing an action.