Student or Learner
What does "s" mean after '90's?
It depends on context. I could mean the years from 1990 to 1999 - those are known as the 90s, or the nineties. It could refer to a person's age if they are between 90 and 99 years old - "He is in his nineties".
There's an ongoing argument about the use of the apostrophe when a number is followed by an "s" to make a plural, as opposed to a possessive. I'm sure we've had plenty of threads on here about it.