These vulnerabilites and Meltdown allow untrusted code to speculatively access data that it shouldn't be allowed to access at all, and use that speculative access to leak data itself. Unlike Spectre this can be (and to some extent has to be) fixed at the hardware level, because the hardware itself is failing to protect sensitive data. This class of vulnerability seems to have been mostly Intel-exclusive so far (with the main exception being one unreleased ARM chip that was vulnerable to Meltdown). There's nothing inherent about modern high-performance CPUs that requires them to be designed this way.

Edit: This slipped my mind, but Foreshadow / Level 1 Terminal Fault was yet another similar Intel-only processor vulnerability that allowed speculative access to data the current process should not be able to access. It's definitely a pattern.