to congeal; to gelatinize; to jellify; to jell; to gell; to freeze
「凝る」 has other readings with different meanings.
to become stiff (of muscles)
to stiffen; to harden
to be into something (e.g. a hobby)
スープが冷めて脂が凝ってしまった。
The soup cooled and the fat congealed.