The term "stag" can refer to a number of different things depending on context.
In some countries, particularly in Europe and North America, it is commonly used as slang for a bachelor party or a night out with friends before one's wedding day. In this sense, the word refers to an event where men celebrate their last moments of freedom before they get married.
However, "stag" can also refer to a male deer that is not part of a herd and typically lives alone. This usage of the term comes from the animal's behavior in nature, as males often live separately from females during certain times of year or when resources are scarce.
In additionally, "stag" can be used to describe an image or photograph that is intentionally blurred or distorted to protect privacy or prevent identification of individuals within the picture. This usage comes from the idea that a deer's eyes will appear large and staring when it is startled or alarmed - hence, "stag" eye effect.