1) An APP in Salesforce is a set of objects, fields, and other functionality that supports a business process.
2) OBJECTS are tables in the Salesforce database that store a particular kind of information. We have two types of objects (i) Standard Object (ii) Custom Object.
3) FIELDS are columns in object database tables. We both standard and custom fields.
4) RECORDS are rows in object database tables. Records are the actual data associated with an object.