Bulk and Encumbered

Bulk

Carrying especially heavy or unwieldy items can make it more difficult for you to move, as can overloading yourself with too much gear. The Bulk value of an item reflects how difficult the item is to handle, representing its size, weight, and general awkwardness. If you have a high Strength modifier, you usually don't need to worry about Bulk unless you're carrying numerous substantial items.

Bulk Conversions for Different Sizes

As shown in the table below, Large or larger creatures are less encumbered by bulky items than Small or Medium creatures, while Tiny creatures become overburdened more quickly. A Large creature treats 10 items of 1 Bulk as 1 Bulk, a Huge creature treats 10 items of 2 Bulk as 1 Bulk, and so on. A Tiny creature treats 10 items of negligible Bulk as 1 Bulk. Negligible items work in a similar way—a Huge creature treats items of 1 Bulk as negligible, so it can carry any number of items of 1 Bulk. A Tiny creature doesn't treat any items as having negligible Bulk.

Encumbered

You are carrying more weight than you can manage. While you're encumbered, you're Clumsy 1 and take a –10-foot penalty to all your Speeds. As with all penalties to your Speed, this can't reduce your Speed below 5 feet.

Source Pathfinder Player Core pg. 269