Curators analyze subgraphs (APIs) to identify subgraphs of high quality. Once a Curator has found such a potentially attractive subgraph, they curate it by signaling on it. In doing so, Curators highlight to Indexers, which subgraphs are valuable and should be indexed accordingly.
Curators can be community members, data consumers but also developers who signal on subgraphs by depositing GRT tokens into a bonding curve. By depositing GRT, Curators mint curation shares of a subgraph, Curators are then eligible to earn a portion of the query fees that the particular subgraph generates. The cryptoeconomic primitive behind this is to incentivize Curators to curate the highest quality data sources.