Guerrilla marketing is an unconventional marketing tactic that uses surprise and creativity to promote products and services. It aims to generate buzz and engagement with audiences rather than rely on large advertising budgets. Some key types of guerrilla marketing include viral marketing, which spreads messaging through social networks, street marketing which engages directly with the public, and grassroots marketing which leverages personal relationships. While lower-cost than traditional advertising, guerrilla marketing requires significant time, energy, and imagination from marketers and may not produce immediate results.