Final answer:
'Ser' is a Spanish verb meaning 'to be' and does not describe any of the options provided like nationality or physical attributes. There might be a misunderstanding in the question as 'ser' relates to essential qualities and identities.
Step-by-step explanation:
The term 'ser' does not specifically describe any of the options provided like someone from the USA or USSR, or traits such as being skinny, fat, short, or tall. It is likely that there might be a misunderstanding in the question as 'ser' is not directly associated with those descriptions. 'Ser' is a Spanish verb meaning 'to be', which is used to describe essential qualities, identities, and natures of subjects, but it doesn't categorize people based on nationality or physical attributes.It is best used to describe someone who is short, someone who is tall, someone who is skinny, or someone who is fat. It is not specifically related to someone's nationality or country of origin.