to come untied; to come apart
to be softened; to be relaxed
「解れる」 has another reading with different meanings.
to become frayed; to become loose
凝り固まった筋肉がほぐれた。
My stiff muscles loosened up.
緊張がほぐれてきた。
I'm starting to relax.
結び目がほぐれて解けた。
The knot loosened and came undone.