What do "cased" and "uncased" mean?

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-05-19.03:45:40.004>
labels = ['3.9', 'docs']
title = 'What do "cased" and "uncased" mean?'
updated_at = <Date 2021-06-23.02:50:12.303>
user = 'https://bugs.python.org/otakutyrant'

bugs.python.org fields:

activity = <Date 2021-06-23.02:50:12.303>
actor = 'andrei.avk'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation']
creation = <Date 2021-05-19.03:45:40.004>
creator = 'otakutyrant'
dependencies = []
files = []
hgrepos = []
issue_num = 44175
keywords = ['patch']
message_count = 8.0
messages = ['393920', '393921', '393954', '393983', '393989', '394098', '394099', '396378']
nosy_count = 5.0
nosy_names = ['rhettinger', 'docs@python', 'josh.r', 'andrei.avk', 'otakutyrant']
pr_nums = ['26865']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue44175'
versions = ['Python 3.9']