spot
The French word 'tache' is used to describe a spot or a stain, usually in the context of a mark on a surface. It can also refer to a task or a job that needs to be done. In the context of a spot or a stain, 'tache' can be used in a similar way to the English word 'spot', for example, 'Il y a une tache sur mon chemisier' (There is a spot on my blouse).
The stain on the sofa is really visible.
In this sentence, 'tache' means stain, and is used to describe a mark or discoloration on the sofa.
Each person has a task to accomplish.
In this context, 'tâche' is used to mean task, and the sentence describes that everyone has a duty or job to perform.
Your birthmark is unique.
The word 'tache' referring to a birthmark in this sentence, illustrating that it can also be used to refer to a mark people are born with.