LTG stands for Lifetime Giving. 
The following Gift Types are used when calculating the LTG total: 

Cash
Pledge
MG Pledge
Stock/Property
Stock/Property (Sold)
Gift-in-Kind
Recurring Gift Pay-Cash
Other
Write Off and MG Write Off amounts are subtracted from the total

Currently, it is not possible to select which Gift Types are displayed on the Giving tab or considered when calculating LTG.