Note: All credit goes to Salesforce, I am just a developer who enjoy playing trailhead and try to make note to myself.In relational database such Oracle,MySql we use table to store data but in Salesforce we use object.Here the summary of term that use in relational database and the term that we use in Salesforce.
Standard Object - objects included by Salesforce by default such as Account,Opportunity,Leads.
Custom Object-object that created by user/developer to support the need of organization.
Fields and RelationshipsIdentitiy - ID
automatically assigned by Force.com.Usually 15 case sensitive characters.It is unique.
Default read only field created by Force.com upon object created such as CreatedDate,CreatedBy,LastModifiedDate etc.
required but not unique, depend on how we want to identify the record.
Created by user .Support type such as autonumber,picklist,text,geolocation etc.
Look up (link to other object) and Master Detail(parent child relationship)
Table is generated using Table Generator.
Source:Understanding Standard and Custom Object