Briefly describe about Field-Level Security in Salesforce?

Record-level permissions are granted at the entity level, but you may have certain fields associated with an entity that contain data that is more sensitive than the other fields. For these situations, you use field-level security to control access to specific fields.

Field Level Security or FLS gives you the provision to restrict particular individuals from accessing super sensitive and confidential information that are located in the records that they can see. FLS security is configured similar to CRUD but it allows the administrators to be able to pre-define the profiles that can see as well as write to most of the fields of the custom and standard objects.