As an admin who manages SharePoint Online (for more information, see SharePoint Online search administration overview), you should also be aware of limits to search. For example, there are limits to the number of entries you can have in a custom search dictionary or the number of rows that are returned as part of a search.
There are two types of limits:
Boundary A number that can’t be exceeded.
Supported A recommended number, based on testing that Microsoft has done, that shouldn’t be exceeded.
If you exceed a supported limit, you might encounter unexpected results or see a significant decrease in performance.
Note: Alphanumeric data in Microsoft Excel documents is indexed and searched, but numeric data is not. For example, the string "PO123456789" would be returned in search results, but the number "123456789" would not.
These limits apply to all SharePoint Online plans.
The following table lists the limits for SharePoint Online search.