Consider a second-order ordinary differential equation

If and remain finite at , then is called an ordinary point. If either or diverges as , then is called a singular point. If either or diverges as but and remain finite as , then is called a regular singular point (or nonessential singularity).

More things to try:

Weisstein, Eric W. "Regular Singular Point." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/RegularSingularPoint.html