The following table provides a listing of all the major fields available in SharePoint lists and Library’s and their corresponding internal names which is always useful when carrying out API queries!

TITLEINTERNAL NAME
Approval Status_ModerationStatus
Approver Comments_ModerationComments
Check In Comment_CheckinComment
Checked Out ToCheckoutUser
Checked Out ToCheckedOutTitle
Checked Out ToLinkCheckedOutTitle
Content TypeContentType
Content Type IDContentTypeId
Copy Source_CopySource
CreatedCreated
CreatedCreated_x0020_Date
Created ByAuthor
Document Created ByCreated_x0020_By
Document Modified ByModified_x0020_By
EditEdit
Edit Menu Table End_EditMenuTableEnd
Edit Menu Table Start_EditMenuTableStart
Effective Permissions MaskPermMask
Encoded Absolute URLEncodedAbsUrl
File SizeFile_x0020_Size
File SizeFileSizeDisplay
File TypeFile_x0020_Type
GUIDGUID
Has Copy Destinations_HasCopyDestinations
Html File Linkxd_ProgID
HTML File TypeHTML_x0020_File_x0020_Type
IDID
ID of the User who has the item Checked OutCheckedOutUserId
Instance IDInstanceID
Is Checked out to localIsCheckedoutToLocal
Is Current Version_IsCurrentVersion
Is Signedxd_Signature
Item TypeFSObjType
Level_Level
MergeCombine
ModifiedModified
ModifiedLast_x0020_Modified
Modified ByEditor
NameFileLeafRef
NameLinkFilenameNoMenu
NameLinkFilename
NameBaseName
OrderOrder
owshiddenversionowshiddenversion
PathFileDirRef
ProgIdProgId
Property BagMetaInfo
RelinkRepairDocument
ScopeIdScopeId
SelectSelectTitle
SelectSelectFilename
Server Relative URLServerUrl
Shared File Index_SharedFileIndex
Source Name (Converted Document)ParentLeafName
Source Url_SourceUrl
Source Version (Converted Document)ParentVersionString
Template LinkTemplateUrl
TitleTitle
TypeDocIcon
UI Version_UIVersion
Unique IdUniqueId
URL PathFileRef
Version_UIVersionString
Virus StatusVirusStatus
Workflow Instance IDWorkflowInstanceID
Workflow VersionWorkflowVersion