The sentence shown in the question above represents a complex sentence. Complex sentences are sentences that have an independent clause and one or more dependent clauses in the composition. In the sentence above, we can see that the clause "is an unusual holiday" is a dependent clause linked to the independent clause "February 2, the midpoint of winter."
Independent clauses are those that manage to emit a coherent meaning on their own, and can be a completely cohesive sentence. Dependent clauses, on the other hand, are clauses that cannot deliver meaning on their own, but need to be complemented by independent clauses in order to be coherent and to be able to convey a message.
