Wikidata uses a query language called SPARQL (pronounced "sparkle"). SPARQL queries allow you to ask very specific questions about information included in Wikidata, and to tap into Wikidata's repository of structure, linked data. SPARQL stands for a "protocol and RDF query language," which is what SPARQL is. As for the "S"...that stands for SPARQL, rounding out a recursive acronym joke. Who knew learning to query would be so funny?
The important thing to know is that SPARQL is a query language for knowledge graphs, which is perfect for linked data.