For both Google and Bing, you can be logged into an account on their sites when conducting searches. In that case, your search is conducted in a "secured context" for privacy reasons, under which your query terms are not available for reports.
To separate the two, Google Analytics uses a capitalization for the site name versus lower case for the search engine name. It uses the Medium label "Organic search" for secured searches in which the query terms aren't available, and "Organic" for those in which they are (i.e., searches conducted when not logged into an account).
Documentation appears to be almost non-existent on this, though the bottom of the following conveys a little in regards to this: Google Analytics - Search Overview
When you sign in to Google.com, your organic search is conducted in a
secure context. If you visit a site from those search results, the
visit is still categorized as organic, but your query terms are not
available in the report. The label (not provided) is used in place of
the query terms.
Referral traffic and cpc traffic are not affected by
the secure context, nor are any of your other statistics like