What does "expedition-weight" mean with regard to clothing?

Question

I'm going on a trip to Alaska in September, including a guided camping/trekking trip in Denali. In the packing list I received from the company, they recommend having an "expedition-weight" top and pants as "extra layers". What, exactly, does this mean?

I've seen "expedition-weight" as a descriptor for fleece tops, but I've never been clear on whether there's a standard definition of the term. Does it only apply to polar fleece, or to other materials as well? Does it refer to a certain thickness/density of fibers, or just to a degree rating?

For what it's worth, this is what the list says under the "extra layers" category (separate from the regular layers of t-shirts, mid-weight synthetic tops and bottoms, synthetic hiking pants, and rain gear):

• Expedition-weight synthetic top
• Expedition-weight or fleece synthetic bottoms
• Fleece or synthetic/down fill jacket

Answer 1

Expedition weight relates to the temperature rating and level of activity. It usually means cold and low activity.

According to REI expert-advice section.

For cool conditions, thermal underwear is available in light-, mid- and expedition-weights. Choose the weight that best matches your activity and the temperature. [...] Like thermal underwear, fleece tops are available in 3 weights:

• Lightweight for aerobic activity or mild climates.
• Midweight for moderate activity or climates.
• Expedition-weight for low activity or cold climates.

According to TrailSpace user trouthunter:

[Relating] to the street clothing you are used to, maybe think of it like this:

• sweater - lightweight
• coat - midweight
• parka - expedition weight

Above freezing your going to be in the lightweight and midweight category, below freezing your going to be in the midweight to expedition weight catagory.