ASUS is shaking up its motherboard lineup by segmenting it into four main brands, each aimed at a different segment of the market. At the top of the triangle, you can see the ROG series. This is the crème de la crème for enthusiasts and "AAA gamers". One step below is the ROG STRIX lineup, these motherboards are intended for core gamers and eSports gamers.
PRIME is intended for professionals and all-round builds, but then it gets a little weird as ASUS is now pushing TUF GAMING for entry-level gamers and first-time PC builders. As TechPowerUp points out, the new TUF series is pretty strange as it conflicts with how the previous TUF lines were perceived:
The TUF series has until now been attributed to moderately expensive motherboards that are designed with very high durability. They are now relegated to the bottom of ASUS' product-stack, targeted at first-time builders and entry-level gamers. These boards are still built "tough" in that they feature high-grade components, but not as many CPU VRM phases as some of ASUS' more expensive boards.