When searching in an Internet search engine or on many databases a limiting tool is the quotation mark. Quotation marks can be used around a phrase or concept of two or more words. Doing this ensures that the concept will be searched for as a whole and not picked apart into separate terms. For example, typing invasive species without quotation marks could potentially retrieve all items that mention invasive, all items that mention species, as well as all items about invasive species. This could lead to results that seem to have nothing to do with your topic, e.g. cardiology diseases in infants or endangered toads in India. For best results, use quotes. For example: "invasive species", "invasive species" and plants, or "invasive species" and "North America".