What is the api limit in salesforce per user per 24 hours?

The API Request Limits documentation goes into a bit more detail into api limit in salesforce

Limits and allocations are enforced against the aggregate of all API calls made to the org in a 24-hour period. Limits and allocations are not on a per-user basis.

Example API Usage Metering Calculations The following examples illustrate API usage metering calculations for several scenarios. For an Enterprise Edition org with 15 Salesforce licences, the request limit is 115,000 requests (100,000 plus 15 licences x 1,000 calls). For a Developer Edition org that made 14,500 calls at 5:00 AM Wednesday, 499 calls at 11:00 PM Wednesday, only one more call can successfully be made until 5:00 AM Thursday.

    In a nutshell, you get 100k requests + (per-licence allocation * # of licences). That makes up a resource pool. Each api request made by a user counts against the pool for 24 hours. Salesforce uses a rolling window, so a request made yesterday (over 24 hours ago) no longer counts towards your limit.

Salesforce also uses their threshold-based approach to limits for api requests (like they do with cpu time, and several other limits). If your pod is "healthy", and you haven't gone over your limit too often, Salesforce can allow you to go over that limit by a bit.