Student or Learner
dear teachers: please explain: Second only to
Not a teacher.
The phrase is basically comparing two people or things and saying that one is the leader, and the other is directly behind.
"Person A is second only to Person B!"
The people are probably involved in the same occupation. That would mean that Person A is one step below Person B, the recognized leader, and above everyone else in the same occupation. It is a compliment to both the person being described and the leader.
It could also be that one company (Company A) has sales figures slightly below the industry leader (Company B). If the company's workers are excited about this, they might say, "Company A is second only to Company B!" as a form of self praise.
Say you wanted to compliment your friend's English speaking abilities.
"Your English is second only to a native speaker!"
That means that maybe native speakers have better English skills, but your friend is just nearly there.
Hopefully I haven't confused you!