A RTW ticket circles the globe. A multi-stop covers several cities without circling the globe, though often times multi-continent. One-ways are single flights. RTW and multi-stop tickets are priced as packages - often 40-60% cheaper than buying the same flights as one-ways.
These three options serve different trip shapes and what a traveler is optimizing for, and picking the right one depends on where you're going and how flexible you need to be.
A round-the-world ticket covers multiple destinations across several continents on a single itinerary, often times, starting and ending in the same country. It's priced as one fare, uses multiple airlines, and typically offers the best per-flight value for trips with 5 or more international stops. The trade-off is that you commit to a general routing structure up front if working with an Alliance.
A multi-stop ticket strings together several flights, usually on one or two airlines, without necessarily circling the globe. This works well when your trip covers one or two regions rather than spanning continents. Flying into Bangkok, then to Bali, then to Sydney, then home is a multi-stop itinerary. It's simpler than a full RTW and sometimes cheaper if your route stays within one airline's network.
Booking one-way tickets gives you maximum flexibility. You buy each flight independently, change plans on the fly, and never commit to a route in advance. The downsides include cost, getting stuck or not going where you want or need to go. International one-way fares are often 60 to 80 percent of the round-trip price, which means 6 one-way flights can cost more than a RTW ticket covering the same cities. You also lose the safety net of having a travel consultant managing your connections.
Here's a rough guide. If you're visiting 5+ cities across 3+ continents, a RTW ticket almost always wins on value. If you're doing 3 to 4 stops in one part of the world, multi-stop is your best bet. If you genuinely don't know where you're going next and value total spontaneity over savings, one-ways make sense, but expect to pay more.
AirTreks specializes in the first two options and can tell you which structure works best for your specific plans within your first consultation.