What is the difference between tart and sweet cherries?

Tart cherries (the ones used to make pies) are shaken off their stems and are more fragile than sweets.   They are immediately soaked in water to prevent breakage and spoilage. Sweet cherries are picked stem and all and usually keep for a longer period of time. Their thicker skin provides more protection. You generally find sweet cherries at your local supermarkets. These are the various types you’ll see:

• Bing cherries are usually very firm with glossy deep red to black or mahogany skin, a white heart (the area around the pit), and a bit of a crunch when you bite into them.

• Lambert cherries are smaller and more tender than Bings. They are a dark red color, soft to the touch, and have a somewhat watery flesh.

• Rainier cherries are yellow to amber, with a pink to red blush. They are more fragile than Bings or Lamberts and have a sweet and mild flavor, juicy flesh, and a white heart.

• Burlat cherries, an early variety that arrives to markets in May,  have a very sweet flavor.

• Royal Ann cherries are a sweet cherry used to make Maraschino cherries.

 
Source(s):
The Unofficial National Cherry Home Page "Cherry Questions" 
Tonytantillo.com "Fruits: Cherries"