program versus engine

What is the difference between avast ENGINE and PROGRAM.
On Xp, the latest update cause my XP box to lock up when touching any program, so I restored an image from 2016 back on the computer and have set program update to manual so that all that automatically all I get are the virus definitions

What is the difference between a engine and a car ?

The engine, is as it it says. the engine.
The program (also called application) is the complete package.
e.g. engine + tires + chassis + body, seats, steer etc

Please post in the correct forum next time as this has nothing to do with your avast account.

@ cub
It is Engine and virus definitions.
Typically the scanning ‘engines’ can be updated as part of the virus definitions update, this saved you doing a full program update.

AND

Program update, which can update things outside of the ‘engine and virus definitions update’ drivers, program updates, fixes, etc. etc.