GoKawiilDolby Digital Plus, also called E-AC-3, still uses lossy compression but supports up to 7.1 channels. A 7.1 soundtrack adds two more surround channels beyond the conventional 5.1 layout, typically giving the system more separation around and behind the listener. The important word is can: DD+ also supports ordinary 5.1 audio, so seeing the newer format doesn't automatically mean more channels are being used. In other words, a Dolby Digital Plus logo isn't an instruction to go shopping for two more speakers.
The newer format becomes particularly useful for streaming. Dolby designed Digital Plus for streaming, on-demand and downloaded content, and services such as Netflix use it for multichannel audio. Its combination of surround-sound support and compression makes it well suited to delivering that audio over the internet.
Dolby Digital Plus can also carry Dolby Atmos. Atmos goes beyond assigning every sound to a fixed speaker channel by including information about where sounds should be positioned around the listener, allowing compatible equipment to adapt the soundtrack to the speaker setup.
That doesn't make Dolby Atmos and Dolby Digital Plus the same thing. Streaming services can use Dolby Digital Plus to deliver Atmos, while Blu-ray discs can instead pair Atmos with Dolby TrueHD, a separate lossless format that preserves the audio data rather than discarding some of it during compression.