The difference between Pile and Pile up

When used as verbs, pile means to lay or throw into a pile or heap, whereas pile up means to form a pile, stack, or heap.

Pile is also noun with the meaning: a mass of things heaped together.

check bellow for the other definitions of Pile and Pile up

Pile as a noun:

A mass of things heaped together; a heap.
Pile as a noun (figuratively, informal):

A group or list of related items up for consideration, especially in some kind of selection process.

Examples:

"When we were looking for a new housemate, we put the nice woman on the "maybe" pile, and the annoying guy on the "no" pile."
Pile as a noun:

A mass formed in layers.

Examples:

"a pile of shot"
Pile as a noun:

A funeral pile; a pyre.

Examples:

"rfquotek Dryden"
Pile as a noun:

A large building, or mass of buildings.
Pile as a noun:

A bundle of pieces of wrought iron to be worked over into bars or other shapes by rolling or hammering at a welding heat; a fagot.
Pile as a noun:

A vertical series of alternate disks of two dissimilar metals (especially copper and zinc), laid up with disks of cloth or paper moistened with acid water between them, for producing a current of electricity; a voltaic pile, or galvanic pile.
Pile as a noun:

An atomic pile; an early form of nuclear reactor.
Pile as a noun (obsolete):

The reverse (or tails) of a coin.
Pile as a noun (figuratively):

A list or league

Pile as a verb (transitive, often used with the preposition "up"):

To lay or throw into a pile or heap; to heap up; to collect into a mass; to accumulate

Examples:

"They were piling up wood on the wheelbarrow."
Pile as a verb (transitive):

To cover with heaps; or in great abundance; to fill or overfill; to load.

Examples:

"We piled the camel with our loads."
Pile as a verb (transitive):

To add something to a great number.
Pile as a verb (transitive):

(of vehicles) To create a hold-up.
Pile as a verb (transitive, military):

To place (guns, muskets, etc.) together in threes so that they can stand upright, supporting each other.

Pile as a noun (obsolete):

A dart; an arrow.
Pile as a noun:

The head of an arrow or spear.
Pile as a noun:

A large stake, or piece of pointed timber, steel etc., driven into the earth or sea-bed for the support of a building, a pier, or other superstructure, or to form a cofferdam, etc.
Pile as a noun (heraldiccharge):

One of the ordinaries or subordinaries having the form of a wedge, usually placed palewise, with the broadest end uppermost.

Pile as a verb (transitive):

To drive piles into; to fill with piles; to strengthen with piles.

Pile as a noun:

Hair, especially when very fine or short; the fine underfur of certain animals. (Formerly countable, now treated as a collective singular.)
Pile as a noun:

The raised hairs, loops or strands of a fabric; the nap of a cloth.

Pile up as a verb (transitive):

To form a pile, stack, or heap.

Examples:

"The kids piled up their boots and coats by the back door."
Pile up as a verb (idiomatic, intransitive):

To collect or accumulate, as a backlog.

Examples:

"The requests piled up while she was away."