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.
"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>"
"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"