Unlike SOQL, which can only query one object at a time and multiple objects only if they are related to each other, SOSL enables you to search text, email, and phone fields for multiple objects simultaneously.
*SOSL is used if we don\’t know in which object the data is present.
*In SOSL we can search data from multiple objects even if there is no relationship among the obejects.
*Works on multiple objects at a same time.
*Cannot used in Triggers.
Cheers!!!