That means it will grow in the absence of air. The spores formed in the absence of air produce a toxin. This toxin is the most deadly we know. There are very few cases of botulism each year. The death rate is high if not treated immediately.
Prevention is extremely important.
Home canning should follow strict hygienic recommendations to reduce risks. Pressure canners should be used for all low-acid foods. In addition, home-canned foods should be boiled for 20 minutes before eating. The botulism spores can only be killed by the high heat which can be obtained in a pressure canner. Infant botulism is a concern for children under one year of age.