'At the weekend', 'on the weekend', 'over the weekend' and 'on a weekend' - Usage & Difference.
Both "at the weekend" and "on the weekend" are used to refer to the same period of time: Saturday and Sunday, their usage depends on the variety of English being spoken.
At the weekend
This phrase is more commonly used in British English.
I like to relax at the weekend.
I went to the park at the weekend.
What are you doing at the weekend?
What do you usually do at weekends?
On the weekend
This phrase is more commonly used in American English.
I like to relax on the weekend.
I went to the park on the weekend.
What are you doing on the weekend?
What do you usually do on weekends?
On a weekend
This phrase is used to talk about something that happens during any given weekend, in a general sense. 'At a weekend' is not used in standard English.
She likes to relax and read books on a weekend.
On a weekend, the city is much quieter than during the week.
Over the weekend
This phrase is used to refer to something happening during the entire weekend, and it's very common in American English.
We went hiking over the weekend.
I finished reading the book over the weekend.