It sounds like you might want to create a traditional project (manually select observations to add to the project) or use an observation field rather than a collection project (automatically adds observations based on the limited options in the filters, can’t manually add or remove observations).
There isn’t currently a way to include observations in a collection project based on tags or keywords used in the description, although there is a feature request to do so. But, as you say, not everyone will add that word as a tag or description.