The superconducting transition temperature, usually written Tc, marks the temperature range where a material enters its superconducting state as it is cooled under specified conditions. Below the transition, the material can lose ordinary electrical resistance and develop its characteristic magnetic response. Above it, the sample normally behaves as a non-superconducting material.
Experiments do not always show a perfectly sharp switch. Researchers may report the onset of the resistance drop, a midpoint, or the point where measured resistance reaches zero. Those definitions can yield different numerical temperatures for the same sample, especially when the transition is broad or the material is inhomogeneous.
Magnetic field and applied pressure can shift Tc, and the current used to make the measurement can affect what is observed. That is why it is misleading to compare two transition temperatures without knowing the measurement criterion and conditions. For high-pressure samples, the distinction between in-cell results and ambient-pressure results is especially important.
When an article says a superconductor works at 151 K, translate that to about minus 122 degrees Celsius and check how Tc was defined. A high onset is promising, but it does not establish that a large, durable sample could carry useful current at that temperature in a commercial device.