"Spring break" is kind of a fixed phrase, at least in the US.
Plus "vacation" is usually used for a contiguous period of vacation. You could say "vacations" if you had days of work mixed into the period you were referring to, so it is multiple "vacations". "Holiday" has connotation of purpose/ memorialized celebration (from "holy-day"). So Christmas and New Year's are separate holidays, but both are in "winter vacation" or "winter break". I think "holiday" might be used a little more loosely in the UK.
Absolutely. In the UK we can use 'holidays', singular or plural, where US English uses 'vacation'. Except at the University of Cambridge, where your 'vacation' is not a holiday - you go home but are meant to keep working!
Yeah there are several questions here which correct 'in the holidays' to 'on the holidays', which is completely wrong.
Because 'каникул' is plural (the singular ends in a, IIRC). So the British English 'holidays' is a more similar translation than the US 'vacation'.
why "what did you do at the time of spring holidays" is incorrect?