An area cleared for cultivation by burning away the vegetation.
Technically, the same as slash-and-burn, a potentially devastating agricultural method, but the term "swidden agriculture" does not have the same negative associations. Most discussions of swidden agriculture try to make distinctions between the levels of ecological impact caused by different slash-and-burn methods.
Also while querying for this post, I saw the term used for more than just the burning of an area for agriculture; it is also sometimes used more generally to refer to the clearing of an area, in relation to alternating periods of farming the land and letting it lie fallow.
Etymology: 1900s, northern English dialect swithen, to burn