The coalesce function in Splunk is used to evaluate each argument in order and return the first non-null value.
This function can be used within an eval expression to create a new field in the results set, which will contain the first non-null value from the list of fields provided as arguments to coalesce. This makes it particularly useful in situations where data may be missing or inconsistently populated across multiple fields, as it allows for a fallback mechanism to ensure that some value is always presented.