What is that's sweet?

That's sweet can refer to a variety of sentiments, generally expressing:

• Affection and Kindness: It's a common response to a thoughtful or caring action, showing that you appreciate the gesture. For example, someone bringing you coffee when you're tired would elicit "That's sweet!". See: https://www.wikiwhat.page/kavramlar/Affection%20and%20Kindness
• Admiration for a Charming or Innocent Quality: It can also be used to describe something that is cute, innocent, or endearing. For example, a child's naive comment might be met with "That's sweet!". See: https://www.wikiwhat.page/kavramlar/Charming%20Quality
• Gratitude: Showing thankfulness for a kindness. It often expresses that you appreciate the kindness. See: https://www.wikiwhat.page/kavramlar/Gratitude

Essentially, "That's sweet" is a positive expression indicating appreciation, fondness, or acknowledgement of a kind or endearing act or trait.