Staying hydrated throughout the day is essential for maintaining good health. Here 'Staying' is a/an -

• Gerund: 
- Verb এর সাথে ing যোগ হয়ে noun এর কাজ করে অর্থাৎ verb ও noun এর কাজ করে, তাকে Gerund বলে।
- Gerund: Verb + ing = noun = Verb + noun.
- It is a word ending in '-ing' that is made from a verb and used like a noun.
- Gerunds don't describe action, they act as noun.

• Staying hydrated throughout the day is essential for maintaining good health. 
- এই বাক্যে 'Staying' Verb এর সাথে ing যোগ হয়ে noun এর কাজ করছে। 

তাই, প্রদত্ত বাক্যে 'Staying' একটি gerund.