Grishma is short for Grishmarutu, the Sanskrit word meaning summer. This is one of the six seasons (ritu), each lasting two months: Vasant (spring), Grishma (summer), Varsha (monsoon), Sharad (autumn), Hemant (pre-winter), and Shishir (winter).
It falls in the two months (Rashi, Saur Maas, or solar months) of Vaishakha and Jayeshtha as per Hindu calendar, or April and May as per Gregorian calendar. It is preceded by Vasant, the spring season, and followed by Varsha, the rainy season.
The word grishma is also used as name for girls. The word grishma is also used for heat.
References
Grishma Wikipedia(Text) CC BY-SA