On the RZ, the current trims in the UK are (in order) Premium, Premium Plus, then Takumi. As you move up, you get a higher specification and more features in the car.
On other Lexus models, there’s often a trim below Premium that’s the base trim - often without a name, but more recently called “Urban”. Lexus have said they’ll be introducing an Urban grade on the RZ later in 2024.
On other models you also get F Sport versions, which are a more sporty version (different seats / wheels / styling / extras etc.), and depending on the Lexus model there might also be a hierarchy there.