The
trigger pull weight is the amount of force that is needed to be exerted upon the trigger for it to fully complete its
travel and trip the
sear which will in turn cause the
firearm to discharge.
A double action trigger pull will be much heavier, sometimes more than twice of that of a single action trigger pull, as not only is the travel considerably longer but your pulling of the trigger also causes the mainspring to compress before tripping the sear to let it go.
Typical DA/SA trigger pulls on a modern semiauto will be about 11 to 12 lbs on the DA pull and about 5 lbs on the SA pull.
The 1911 being a single action pistol with a stirrup type trigger has the sweetest trigger pull of all, and I mean all. On a very well tuned 1911 there is no take up and the trigger can be made to break at about 3.5 lbs. It's as if you just slightly rest your finger on it and it will fire, providing very good accuracy as there is very little muscle tension on the firing hand.
Most other pistols with SA capability can not, and will not ever have the sweet pull of the 1911 as they use a swivelling trigger to also allow for DA shots. This design will always have some sort of take up and will have a miniscule amount of creep as the transfer bar isn't as rigid as the stirrup type of trigger.
For a service grade or carry firearm, a minimum of a 5 lbs trigger pull in single action is more or less the safe compromise.