Trigger.isExecuting is to determine that your current context for the Apex code is a trigger, not a Visualforce page, a Web service, or an executeanonymous() API call.
Here is an example of Apex Class, this class can identify current context for the Apex code is a trigger using Trigger.isExecuting.

Apex Class:

public class AccountHandler
{
    public Boolean handleAccount(List<Account> accList){
        
        System.debug('Trigger is executing : ' + Trigger.isExecuting);
        
        if(Trigger.isExecuting){
			//Do what ever you want to do as part of the trigger invocation
        }
        else{
            //Do what ever you want to do if the call originated from different context, such as from controller.
        }
        return Trigger.isExecuting;
    }
}

Apex Trigger:

trigger AccountTrigger on Account (before insert, before update){
    AccountHandler handler = new AccountHandler();
    handler.handleAccount(Trigger.New);
}