Please define the term lock and load?

It is actually "load and lock", but most people know if the other way from TV and the movies. It means to load your weapon with the appropriate rounds/magazine and lock a round into the chamber, ready to fire (preferably with the safety on, although that depends on the tactical situation.)

Refers to the Loading Procedures of a M16 / M4 Weapon

1) Visually inspect rifle to ensure weapon is on safe and no ammunition is present in chamber or receiver

2) Send Bolt Carrier (containing firing pin & bolt) forward (LOCK / Forward) by slapping bolt release tab on left side of weapon.

3) Insert loaded ammunition magazine into weapons Lower Receiver until magazine locks in place. (LOAD - Magazine)

A) NOTE - Having Carrier Bolt forward first prevents top ammunition round in magazine from possibly becoming dis-lodged when mag is inserted.

4) Pull charging handle fully to the rear and release (allow bolt to slam forward) - thus chambering a round of ammunition.

5) Place weapon selector switch from SAFE to SEMI (Fire Mode)

6) Take Aim at Target and Shoot (pull weapon trigger)

This is Air Force Weapons Skills-Rifle handling procedures from AFMAN 10-100

I'm currently in the Army.

I know this question. lol

It simply means to "lock" the bolt of the weapon to the rear of the gun...(that way the magazine can slide in)

And load, is when you insert the magazine, into the magazine-well of the weapon.

Hence, "Lock, and Load"

It means fill up your weapon make sure the bullets are secure and be prepared to fire