Bog mat
Also called Timber mat, Swamp mat, Access mat
Site shorthand for a heavy timber mat, typically hardwood baulks bolted or banded together, laid so plant can travel or stand on soft, wet or unmade ground. Bog mats are access and ground protection products first: they are usually supplied by size and species rather than against a published safe working load, which is the difference that matters when one ends up under an outrigger.
In practice
The name describes the duty rather than the product, so what arrives varies — new or second-hand, ekki or another hardwood, bolted or banded, often already worked hard elsewhere. For the job it is meant for, that is fine. It becomes a problem the moment an unrated mat is treated as a spreading element in a calculation, because there is no figure to put in: timber capacity varies with species, grading, moisture content, splits and previous service, and a used mat cannot be inspected back to a number.
Where this comes from: UK site and hire-desk vernacular. What any particular bog mat will carry is a question for the supplier of that mat and the grading it was sold against; nothing here rates a timber product.
Where it matters on site
The risk is substitution. Mats laid for tracking end up under the feet at set-up because they are already there and they look substantial. If a mat is to carry an outrigger reaction it needs a rating somebody will stand behind and a temporary works design that used it; where the mats on site have no rating, they are ground protection, and the spreading element still has to arrive — or the reaction has to come down until the ground alone will take it.