Yes, PACK is a Scrabble word!

Letter values in Scrabble US: P 3, A 1, C 3, K 5.

Is it a valid word?

PACK is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a large indefinite number
a complete collection of similar things
a convenient package or parcel (as of cigarettes or film)
an association of criminals
an exclusive circle of people with a common purpose
a group of hunting animals
a cream that cleanses and tones the skin
a sheet or blanket (either dry or wet) to wrap around the body for its therapeutic effect
a bundle (especially one carried on the back)

arrange in a container
fill to capacity
compress into a wad
carry, as on one's back
set up a committee or legislative body with one's own supporters so as to influence the outcome
have with oneself; have on one's person
press tightly together or cram
hike with a backpack
press down tightly
seal with packing
have the property of being packable or of compacting easily
load with a pack
treat the body or any part of it by wrapping it, as with blankets or sheets, and applying compresses to it, or stuffing it to provide cover, containment, or therapy, or to absorb blood

Also: large number, inner circle, face pack, tamp down, load down.