Spam is junk or unwanted email, such as unsolicited promotions and chain letters. Non-spam email is often called ham. section 1.3
Spam detection classifies email as spam or ham. A naive Bayes model estimates these probabilities from email features; one example uses words, where “lottery” is more likely in spam than “meeting.” section 8.2
Estimating spam probability
In a sample of 100 emails, 20 are spam, giving a prior estimate of 0.2. Among 20 emails containing “lottery,” 15 are spam, so the estimated probability of spam given that word is 0.75. section 8.2


