Attention Bucket Shoppers: Here’s Latest Airline Lingo : Consumers: Ticketless travel and other innovations behoove travelers to learn the vocabulary of an ever-changing business.

The airline business keeps changing. In just the first four months of this year, ticketless travel has advanced, travel-agent commissions have been capped and service fees have proliferated.

With these changes come amendments to the travel trade’s working terminology--a collection of words and phrases that often intimidate and confuse consumers. Here’s a quick update on vital vocabulary for air travelers.

Advance purchase: Usually a requirement when you’re buying a discounted restricted ticket. Advance-purchase requirements are most commonly seven, 14 and 21 days. In a recent trend, several airlines adjusted their most heavily discounted fares to require purchase 21 days in advance, rather than 14.

Bucket shops: Also known as consolidators, these are businesses that quietly buy up excess tickets from airlines, then sell them at reduced rates, either to travel agents or directly to consumers. Usually the tickets are heavily restricted, and frequently the consolidators’ offices are low-margin, high-volume operations.

Charter flight: A less costly alternative to flying on a regularly scheduled major airline. The drawbacks: Charter flights (often arranged by tour operators rather than airlines) are usually more crowded than scheduled commercial flights, and usually impose more restrictions on travelers and fewer obligations on the charter operation. For instance, U.S. Department of Transportation officials note that a tour operator or airline can cancel a public charter flight for any reason up to 10 days before departure. Similarly, public charter flights may be delayed as long as 48 hours before the operator is obliged to offer refunds.

Code-sharing: A marketing pact in which two airlines collaborate to make themselves look larger than they are. The carriers share codes in listing flights, so that the carriers’ flights will pop up more often when travel agents search computerized reservation systems. Thus you may buy a seat on Airline A’s Flight 1, then arrive at the airport to find that the plane in question has Airline B’s name on the side, an Airline B crew, and has been sold as both Airline A Flight 1 and Airline B Flight 2.

Commission cap: In February, most major airlines announced that instead of paying 10% commission to travel agents on domestic fares, they would pay no more than $50 on round-trip fares of $500 or more, $25 on one-way tickets of $250 or more. For the agents’ response, see “service fees” below.

Commuter flight: Planes that hold fewer than 31 passengers are widely known as commuter craft, and in recent years have had higher accident rates than have larger planes. (The Federal Aviation Administration last month proposed new safety standards aimed at putting commuter flights on a regulations par with larger, more closely monitored commercial aircraft.) Commuter craft often carry four-digit flight numbers, instead of the three digit generally used by larger planes.

Direct flight: A flight that involves one plane, but more than one stop.

Elite level status: For this country’s most frequent fliers, this is a sort of Grail. Elite programs carry various names, such as AAdvantage Gold at American and Premier at United. At both carriers, members must fly 25,000 miles a year, excluding credits racked up in phone bills, hotel stays and the like. Program perks include a spiffy card, top priority in receiving seating upgrades (from business to first class, for instance), and a boost of 25% in the overall mileage credit you accrue per flight. For those who reach 50,000 miles or per year, the perks get even grander.

Full-fare coach: The most expensive of coach tickets. Most of these go to business travelers, who can, therefore, change flights or get refunds at no cost, and who are often upgraded if first- or business-class seats are empty. As this month began, a round-trip LAX-Atlanta flight on Delta ran $451 for a restricted coach ticket (nonrefundable, requiring a Saturday stay and 14-day advance purchase), and $1,301 for full-fare coach. The difference is comparable among other carriers.

Load factor: The airline equivalent of hotel occupancy rates. A key consideration when airlines use “yield management” strategy in setting widely varying prices for similar seats. Service fees: Imposed by most major travel agencies since the major U.S. airlines announced commission caps. Fees tend to run $10-$20 for an airline-ticket-only purchase.

Ticketless travel: Also known as “electronic ticketing.” In a process that reduces airline paperwork and expenses, “ticketless” travelers make reservations by phone (either directly with the airline or through a travel agent), give their credit card number for payment and receive a confirmation number--but no ticket in the mail. On flight day, the traveler arrives at the airport, gives his or her name (and confirmation number, if necessary), shows identification, gets a boarding pass and boards. Southwest, which started ticketless testing last September, now issues 15% of its tickets that way, and offers the option on all flights. United unveiled the process with its Shuttle by United service in California Nov. 1, and aims to make ticketless travel an option on domestic flights in coming months.