A frequent term mentioned in strategies, meatshields are units whose function is to draw and absorb enemy fire. They are generally placed ahead of other troops, due to the fact that most enemy units will acquire the nearest target to fire at (for those that don't, see eliminators). Just how far ahead in placement, though, is something that must be considered with care, as many explosive-wielding enemies have large miss areas around their targets, so that their projectiles could still land far behind the meatshield and hit your main force.
Ideal meatshield units are those who can either withstand large amounts of fire or come at a good value, such as the Sherman Tank, Jeep, Medic or Frenchie. Bunkers are very useful for protecting infantry meatshields, as is Heroism.
The most common set up of a meat shield involves a bunker with a gunner, two frenchies, and a medic inside of it. The gunner, after twenty exp or so, will be a great Anti-Infantry unit especially since it cannot get gibbed because it is in a bunker unless the bunker itself gets destroyed. The two frenchies will soak up any bullets and will direct tank fire to your bunker while the medic will heal your frenchies back to 100 hp as long as they are alive.
Meatshields do not explicitly exist in any army... if you consider it, who would want to be known as a meatshield? That said, in lower key operations bodyguards can take up this role, putting themselves as a physical barrier between a threat and their client.
In Other Games
Many RPG, co-op, or shooter games offer a 'tank' class, usually designed to be a meatshield against enemy attacks. Such a practice is often simply called "tanking hits", and is pertinent to classes or players with very high defensive prowess, accompanied usually by low speed, low intelligence, and a decent amount of attack power, usually brute strength.