The Mechaber mentions not to take haircuts from Pesach until Shavuous, until the 34th day of the omer (the Rama says 33rd).
Question: Why does the Mechaber bring in Shavuous? He could have just said: “Don’t get a haircut from Pesach until Lag Baomer” – what does Shavuous have to do with anything?
This is an interesting, technical point. The Mechaber is actually quoting the Tur that says from Pesach until Shavuot. The Bais Yosef brings however from the Avudrohom that we may make weddings from lag baomer just like taking haircuts. This may be why he brings this terminology.
As a side point see Kaf Hachim 493-11.