When you buy travel insurance you can choose from 2 types of policies. Single Trip and Annual Cover.
Single Trip Travel Insurance covers you for a single trip that originates and ends in Singapore.
Annual Travel Insurance covers you for all trips starting and ending in Singapore. Each trip generally should be for less than 180 days.
You should consider buying Annual Travel Insurance if you travel frequently (more than 3 to 5 times a year). You will enjoy significant savings, and you won’t have to worry about purchasing travel insurance every single time as you’ll be covered for the entire year.
Also, Read Single trip vs Annual Travel Insurance