Questions about receiving a higher tier of service than originally contracted, such as flying in a more premium cabin or receiving a higher category of room at a hotel.
An upgrade, in travel, refers to a customer being granted a higher tier of service than originally contracted.
Not every improvement in the travel experience is technically an upgrade. Most passengers would consider moving from a middle seat to its adjacent aisle seat as an improvement, but this would not be categorized as an upgrade in the airline's contract of carriage; the airline does not sell them as separate categories of service. By the same token, someone who values legroom above all else may refuse an upgrade from an exit row in economy on a certain aircraft to a bulkhead row in business class, considering it a degradation of her travel experience.
Vendors often tie the possibility and availability of upgrades to the level of participation in their loyalty-program. Elite members of the program may receive certain automatic upgrades, such as a larger category of vehicle than reserved when renting a car, or being eligible for a first class seat when paying an economy fare on certain airline routes. The program may also allow the use of points or miles to request or secure upgrades in advance. Third, vendors may have published or unpublished policies whereby their agents can grant upgrades to others, such as people paying very high fares.
Each vendor has its own rules for determining who qualifies for what kinds of upgrades, and in what order they are processed. In most cases, therefore, questions with this tag should also use the tag of the company or program in question.
Questions about the likelihood of upgrades (e.g. What are my chances of getting into business class on BA283?) are likely to be closed as opinion-based or too narrow, as such information is constantly shifting, and any authoritative answer would be considered proprietary information by the vendor. They should be worded instead as questions about strategies for improving the chance of an upgrade, or about the kinds of paid upgrade options available.