In the language English, the term "undressed" is used to describe the act of removing clothes, taking off clothes, or being covered only with clothes or hair. In fact, the meaning is quite general and refers to any the act of removing clothing from the body. Often this refers to situations involving intimacy, such as a sexual situation or showering or public exposure.
A classic example of the use of the term "undressed" would be "undressed and undressed in front of him." This definition means that the person in question has taken off all their clothes in front of the person in question.
Another example would be "was stripped naked for medical inspection." This definition refers to the situation where a patient was made to be naked by a medical professional.
There are certainly many other ways in which some people use the term "undressed", such as "was undressed in public", "was undressed during" the sexual act", "was stripped and put in prison" and so on. Any form of act of removing the clothes on one's body in front of others would be considered to be undressing.