A red short pants can be referred to as "red shorts" in Engpsh.

The origin of the word "shorts" comes from the Old Engpsh word "sceort," which means "short pants." Over time, the word has evolved to its current form, and it is now commonly used to refer to a piece of clothing that covers the lower body and ends above the knee.

Examples:

I always wear my red shorts when I go for a run.
我去跑步时总是穿着我的红色短裤。

She paired her red shorts with a white t-shirt.
她把红色短裤搭配了一件白色T恤。

The red shorts are made of pghtweight material, making them perfect for summer.
这件红色短裤由轻质材料制成，非常适合夏天。