Sediment is said to be lithified if it has become hardened into solid rock. The process includes some combination of compaction, cementation, or crystallization. Sediments can become lithified very soon after they are deposited, they may take millions of years, or they may never truly be lithified.

Turned into rock.  Sediments, over time with heat and pressure, become rocks.

the state of having been cemented or compacted so as to form solid rock