Dust transactions are cryptocurrency transactions involving a minute amount of crypto. When the value of a transaction is less than the cost of spending it, it's referred to as "dust." The transaction cost to move or use the dust exceeds its actual value, rendering it economically impractical to spend. Dust transactions can be used maliciously in dusting attacks, where small amounts are sent to many wallets to track and deanonymise users.
Decentralised applications, or dApps, are applications that run on a decentralised network, such as a blockchain, rather than relying on a single central server. This eliminates a single point of failure, enhancing security, transparency, and reliability.