HDMI 2.0 is an improved standard for AV connectivity and the heir apparent to HDMI 1.4 (released back in 2009). You'll need an HDMI 2.0-compatible HD TV if you're interested in watching the full range of 4K Ultra HD source material in the future.
While HDMI 1.4 has a throughput of 10.2Gbps, it's only enough to support a 4K resolution of 3840 x 2160 pixels at 24, 25 and 30Hz or to display full 4K (4096 x 2160 pixels) at 24Hz. The 2160p24 and 2160p30 formats might be good enough for movie playback, but they fall short of the 50/60Hz required for 4K TV broadcasts and future Ultra HD gaming.
HDMI 1.4 also only supports 8-bit colour at 4K. HDMI 2.0 improves upon this, offering 10 to 12-bit colour depth at Ultra HD resolutions.