The long run is the single longest training run in a weekly schedule, usually done at an easy, conversational pace. It's the backbone of endurance training for half marathons and marathons, building the stamina and mental toughness needed to cover race distance. It's typically run once a week, often on a weekend.
It's the longest run in your weekly schedule, typically building up toward 29 to 32 kilometres for marathon training. It's run at an easy, sustainable pace, not race pace.
Slower than you think, usually 60 to 90 seconds per kilometre slower than marathon goal pace. You should be able to hold a conversation for most of it.
Once a week is standard for most training plans, usually on a Saturday or Sunday when you have time to recover afterward. Doing it more often risks overtraining and injury.
It trains your body to burn fat efficiently, strengthens connective tissue, and builds the mental resilience to keep going late in a race. No amount of shorter, faster running fully replaces that adaptation.
Yes, treat a few long runs as dress rehearsals for race nutrition and hydration. It's the best way to find out what your stomach actually tolerates before race day.