What is the meaning of "service bits" in Bitcoin?

// Keep in mind that of those that support the service bit prefix, most only support a subset of
// possible options.
// This is fine at runtime, since we will use them again as a single capture if they are not compatible with
// the service bits that we want, but we should update them to support all the service bits needed by anybody
// Release as soon as possible to avoid it when possible.

Reference: https://github.com/bitcoin/bitcoin/blob/master/src/chainparams.cpp#L116