The phrase "is somewhat" is used to indicate that something is true to a limited extent or degree. It suggests a moderate degree of something rather than being absolute or extreme. For instance, if you say "It is somewhat cold outside," you mean that it's a little chilly, but not extremely cold.
The phrase "is somewhat" comes from the combination of the copular verb "is," which is the third person singular present form of "be," and "somewhat," which is derived from the Old English "sum hwæt," meaning "some thing" or "a certain amount."