The different letters represent where the row breaks are. Depending on the row, the ticket pricing is typically different:
Sections 101-104 and 127-130: All rows are "LB"
Sections 105-106 and 125-126: Rows 1-30 are "PL"
Sections 105-126: Rows 31 & up are "LB"
Sections 112-119: Rows AAA-CCC are "DC"
Sections 107-124: Rows A-E are "PF", F & above are "FC" and 1-30 are "PL"
Dugout Club (DC)
Lower Box (LB)
Premium Lower Box (PL)
Premium Field Club (PF)
Field Club (FC)