What it means
Often translated “sect” or “party”, this word generally means a subdivided group with their own interests. Early Christians were called a Jewish sect (Acts 24:5, Acts 28:22). It’s also interesting to note that in 1 Cor 11:19 we are told that there must be sects among us in order for “those who are genuine” to be recognized.
Acts 20:30 also warns us against people who rise up speaking twisted things who “draw away disciples after them”. 1 Timothy 4:1 warns us against the same type of thing, as does 2 Peter 2:1 (which actually uses the word “hairesis”).
This is also what Paul wrote against in 1 Corinthians 1:10-17.
From this word study, I think an interesting question to ask from a study of this word would be; “Why do we have denominations?”
Where it’s found