To char is to burn or blacken something so that it’s like charcoal but still tasty. A char is something that has been burned in this way.
To char is to burn something on the outside. If you've ever eaten a hot dog or hamburger cooked over an open flame, it was charred. Many people like the taste of char-grilled meat. To char doesn’t usually mean to burn all the way, just enough to blacken. Unfortunately, char can also mean to reduce to charcoal — if there's a house fire, couches and chairs could be charred. Not so delicious.