Discrimination is the unjust treatment of people with a protected characteristic. It involves treating someone differently or worse than someone else on the basis of that protected characteristic.
Even if you did not intend to treat someone less favourably or to discriminate against them, if you treat someone differently because of a protected characteristic, this could be considered as discrimination.
Examples of discrimination include, but are not limited to:
Such forms of discrimination can be considered offensive. It is important then to choose your words carefully to avoid disrespecting someone.