Lettuce is a leafy green vegetable belonging to the daisy family, commonly grown as a cool-season crop. It's primarily composed of water (about 95%) and provides essential nutrients including vitamin K, vitamin A, and folate, while being very low in calories.

There are several main types of lettuce: iceberg (crisp with mild flavor), romaine (sturdy leaves, slightly bitter), butterhead (soft, buttery texture), and leaf lettuce (loose, tender leaves). Lettuce prefers cool temperatures between 60-70°F and can be grown in spring and fall in most climates.

The vegetable is harvested when heads are fully formed but before flowering occurs, typically 70-100 days from planting depending on the variety. Lettuce is widely used in salads, sandwiches, and wraps, and should be stored in the refrigerator to maintain freshness and crispness.