SCP stands for either Special Containment Procedures or Secure, Contain, Protect, which is the SCP Foundations Motto.
The SCP Foundation is a large organization specializing in containment of anomalous creatures or objects to protect mankind and to study them to create scientific breakthroughs.
They have many different Facilities and containment areas across the world, most of them specializing in containing certain types of anomalous creatures or objects.
There are 3 main classes of SCPs, Safe, meaning that the object is either mostly harmless, easily contained or both. Euclid, objects or creatures that are dangerous, have an unknown movement pattern or have some other effect. These aren't as easy to contain as Safe class SCPs, but aren't as hard to contain as Keter class SCPs. Keter, meaning that the object is dangerous to mankind, has powerful mind-control abilities, can cause an XK Class End-Of-The-World Event, can cause a ZK Class Reality Failure event, can extremely rapidly reproduce or regenerate, or have other extremely dangerous effects. These types of SCPs are extremely hard to contain.
Anomalous Items or Creatures that are not dangerous or anomalous enough to be an SCP are known as Anomalous Items.
Site 19 is a secure facility used by the Foundation. This is the largest containment Site they currently have.
SCP-914 is a Safe class SCP. If an item is placed into it, it produces an item and the original item placed into it is either lost, or modified. It has 5 settings, Rough, which usually dismantles and destroys items. Coarse, dismantles item. 1:1, gives an item of similar make or worth. Fine, which usually produces a better item, however, slight anomalous properties have been documented. Very Fine, items created are usually of Anomalous Properties. Item is potentially dangerous, however extremely easily contained and protected.
SCP-173 is an Euclid class SCP. It is a concrete, rebar sculpture that moves when not looking at it. When it gets close to a human or otherwise living creature, SCP-173 will snap it's neck and kill it, or attempt to. It is dangerous and hostile, and can move through vents, but can be contained fairly easily by putting it in a containment chamber, although Containment Breaches involving it have happened before.
SCP-682, a Keter Class SCP. It is an extremely large reptilian creature that is extremely hard to damage, regenerates at extremely fast rates and can adapt to most situations by either becoming immune to the thing hat is damaging it, or using it's abilities. It is extremely hostile towards humans and animals and is almost impossible to contain.