Difference between TRIACs holding and Latching current
When a gate signal is applied to a triac/SCR/thyristor it won't latch until the main current flowing through the device has reached the "latching" level. It will conduct if the gate signal is sufficient but, if you remove that gate signal before the latching current level has been reached then it will stop conducting.

Once latched, the gate signal can be removed and it will stay conducting (latched) until the current falls to the level called the holding current. Clearly the "holding" current is less than the latching current.