An odd number.
"The doctor noted that his behavior was a result of ODD, which stands for Oppositional Defiant Disorder."
Initialism of oppositional defiant disorder.
In plain English: An odd is a number that cannot be divided evenly by two, meaning it always has one left over when you split it up.
"She found an odd in her pocket that she had never seen before."
Usage: Do not use "ODD" as a standalone noun to refer to the initialism for oppositional defiant disorder; instead, write it in all capital letters only when explicitly defining or referencing the medical acronym within a sentence. In general writing, reserve the term "odd" as an adjective to describe something strange or unusual rather than treating it as a specific noun label.
beyond or deviating from the usual or expected
"a curious hybrid accent"
"her speech has a funny twang"
"they have some funny ideas about war"
"had an odd name"
"the peculiar aromatic odor of cloves"
"something definitely queer about this town"
"what a rum fellow"
"singular behavior"
Differing from what is usual, ordinary or expected.
"The sudden silence in the busy cafeteria felt odd to everyone who walked by."
In plain English: Odd means something that is not even or doesn't fit in with what is expected.
"The old man had an odd habit of humming tuneless songs while walking his dog."
Usage: Use "odd" to describe something that is strange, unusual, or not in line with normal expectations. Avoid confusing it with numbers that are not divisible by two when referring to quantity.
The word "odd" comes from Old Norse words meaning a point or an additional number. Its original sense of being left over after division into pairs likely developed from the idea of a sharp point sticking out.