In the US, many events are "sponsored by" businesses. For instance, a local opera house's season may be sponsored by a local bank--in other words, the bank contributed a significant amount of money to help the opera put on its shows that season.

Industry conferences also normally have sponsors: companies in that industry, or companies that serve those in the industry, which provide funding to help the conference happen.

Companies sponsor events for several reasons, with a major one being that in exchange for sponsorship, they get good publicity. Their name and logo may be on the marketing materials for the event; they might get a large, attention-getting booth at the conference; etc. The basic gist is that the sponsoring company, by being known as a sponsor, gets good publicity that improves its reputation and/or its bottom line (income).
Link: https://blog.bizzabo.com/event-sponsorship#what

What Hugues' text is saying is that a contribution to a charity counts as a "Charitable Donation" only if the contributor does not receive any business benefits in exchange. One type of benefit that cannot be receive is "sponsorship promotion." In other words, if X Business contributes money to a charity, and as a result that charity lists X Business as a sponsor in its advertising, marketing materials, etc., then the contribution does not count as a "Charitable Donation."

The "promotion" here refers to publicizing the fact that Company X contributed money to the charity. In other words, promotion of Company X's sponsorship:

"As an [event] organizer, it is your responsibility to foster a strong relationship with your sponsors and to provide them with enough value to convince them to partner with your event in the future. The best way to provide this value is to promote your sponsors..." https://blog.bizzabo.com/examples-of-event-sponsorship-promo...