Salesforce Object Query Language(SOQL) and Salesforce Object Search Language (SOSL)

SOQL is similar to the standard SQL language but SOQL is more customized for the Force.com platform. To read a saved record from Sales force, Sales force Object Query Language (SOQL) is used.

Sales force Object Search Language (SOSL) is used to construct text-based search queries against the search index.
SOSL searches are faster and can return much more relevant results.

SOQL can only query one object at a time, but a single SOSL query can search all objects which includes custom objects.