IndexDefs contains definitions for each index the current table has. IndexDefs is a collection of TIndexDef objects. Each TIndexDef object contains the definition for one index. 

Inspect IndexDefs at runtime to get information on a given index. Use an index with IndexDefs to address a specific TIndexDef object. Use properties of TIndexDef to evaluate various index attributes. The example below retrieves the fields list for the third index of the table accessed through the component ADOTable1.

ADOTable1.IndexDefs.Update;
StrVar := ADOTable1.IndexDefs[2].Fields;

ADOTable1->IndexDefs->Update();
StrVar = ADOTable1->IndexDefs[2] ->Fields;

Call the Update method (TIndexDefs) prior to inspecting the property to ensure it contains the most current index information for the table. 

TIndexDef 

TIndexDefs 

Update