What does the term obligatory precaution (Ihtiyat e wajib) mean?
Can the follower oppose it? And if it cannot be opposed, then why there is need to use this term?

Ihtiyat wajib — precautionarily obligatory. Its significance is the same as that of wajib with the difference that in the problems where a mujtahid says it is "precautionarily obligatory", one has the option of leaving his taqlid (following) in this particular problem and following the rulings of the second-best mujtahid in that problem.