Option: An out-of-the-box feature that is available in S4S but should not be installed unless required.
Module: An S4S feature that is not out-of-the-box and is a paid extra.
Save Action: A code library that executes when a web form is submitted by a website visitor. This is also called a Submit Action
Security Connector: An optional feature that lets website visitors log into the Sitecore website using credentials stored in a Salesforce Contact or Lead record. It requires a package to be installed in Salesforce.
Experience Forms or WFFM Forms: Types of Sitecore web form. S4S can push the form data to Salesforce and includes significant includes functionality to support these forms
S4S Installation Overview