It takes more thought than you’d think to figure out which years are leap. Years divisible by 4 are leap, except for the century, i.e. years ending in -00 are not leap years, unless the first 2 digits are also divisible by four. Got it?
So 1700 is not a leap year, but 1600 is. That’s why the year 1900 was not, but 2000 was. Don’t stress, you won’t have to worry about getting it wrong until 2100 (which is not leap).
When Pope Gregory XIII declared the first leap year to be 1588, the Protestants were ruling England and they rejected the law, saying it was too Catholic. The problem was that on the day after the 28th of February the rest of the world had calendars that acknowledged the 29th. So Protestant Brits just ignored the day, as if the law and custom didn’t apply to them. So a superstition arose that the other laws and customs didn’t apply either. Hence the name ‘leap year’ as it was the day that ‘leapt over the law.’ Sometimes non-conformity can be taken too far.
One such custom which was leapt over was that of marriage proposal etiquette. It was customary for a gentleman to propose by sending a glove to his true love. If she was seen wearing it at church the following Sunday, she had accepted the proposal.