Additional Surveillance Measure (ASM) is an initiative by the Securities Exchange Board of India (SEBI) and exchanges to enhance market integrity and safeguard investors' interests. There are certain criteria that are used to move stocks to the ASM category, which can be found in the NSE FAQ (PDF)
source link given below. Stocks under ASM are divided into two categories, i.e. long-term ASM (WEB) and short-term ASM (WEB).