Delete 100 lines forward from (including) the current one

delete 100 lines forward from (including) the current one

repeat dd (delete current line) 100 times:

100dd
delete from current line to 99 lines forward

d99j
delete 100 lines backwards from (including) the current one

d99k
delete lines in a specific range by line number

:1,100d
delete lines in a range beginning with the current line