In standard exoplanet naming, the first planet found around a star is usually assigned the lowercase letter b.
The convention extends the system used for multiple-star designations. The host star is treated as the primary component, effectively “a,” so the first planetary companion receives “b,” the next receives “c,” and so on. Thus 51 Pegasi b was the first planet discovered around 51 Pegasi, while a system with several discoveries may contain planets such as 55 Cancri b, c, d, and e.
The letters normally follow discovery order, not distance from the star. If multiple planets are announced together, naming practice can use their orbital order, which is one reason the sequence should not be interpreted as a simple map of the system.
Binary and circumbinary systems add complications. A planet orbiting one member may receive a designation such as 16 Cygni Bb, while circumbinary planets can be written with an “AB” component designation. The lowercase b is therefore standard, but “first” refers to discovery within that naming system—not necessarily the innermost planet.