An operation is case insensitive when uppercase and lowercase characters are equally treated.
An operation is case sensitive when uppercase and lowercase characters are treated differently.
"Btw a case-sensitive search done with removing i is much faster than a case-insensitive search"
from question "Fastest way to search for a text string in all files & directories (recursively), then output the directory and filename"
"This tiny overhead on add is vastly outweighed by the savings on lookups since all programmers should know and understand that case-insensitive compares are vastly slower than case-sensitive especially with unicode - the cpu can t just do a block compare of data but must check each pair of characters specially even using a table look-up this is vastly slower"
from question "Finding an item in a List<T>"