This is the 12177th most frequent Polish word.
marzec
March.
Here, 'marcu' represents the locative form of 'marzec', used after 'w' to indicate time within the month.
W marcu zwykle jest jeszcze chłodno, ale dni stają się dłuższe.
In March, it is usually still cold, but the days become longer.
Here, 'marzec' indicates the specific month in a past time reference about the year's weather.
Marzec tego roku był szczególnie deszczowy.
March of this year was particularly rainy.
Here, 'marzec' is used as a noun to indicate the name of a month.