WikiProjects are dedicated to addressing information quality, content gaps, maintenance, and building community on Wikidata. Editors join WikiProjects to improve specific areas of Wikidata.
Like Wikipedia, some topic areas on Wikidata are more comprehensive than others. WikiProjects are the first place to go to learn about the state of whatever topic you are interested in on Wikidata.
Every WikiProject on Wikidata has its own set of editors and standards to cater to the needs of that particular topic. Typically WikiProjects contain data models, property usage, completion statistics, and a conversation about that particular topic.
Note: WikiProjects exist on both Wikidata and Wikipedia. They may have the same titles, but they are different WikiProjects. The WikiProjects on Wikidata focus on Wikidata-specific issues like modeling items, creating new properties, and evaluating gaps in the disciplines. WikiProjects on Wikipedia discuss article content, track article statistics (like Good Articles or Featured Articles), and gather Wikipedia-specific templates.