"low current", "high efficiency", "high intensity" LED's
The terms listed do have relevance, albeit limited: There are no globally mandated benchmarks, I believe, for what constitutes low current, or high intensity in an LED.

In general, "middle-of-the-road" LEDs are usually specified at 20 to 25 mA. Thus, an LED that glows at nominally "full" intensity at 5 mA (maybe even 10) would be considered low current.

Over successive generations of LED technology, the luminosity per Watt for LEDs has increased steadily - to the extent that "Haitz's law" observes that light generated per LED in each color increases by a factor of 20 per decade. Some manufacturers  market their 100 Lumen/Watt and better LEDs (post 2010) as "High intensity", but that too is clearly a moving target.

High efficiency in LEDs - (warning, moving fully into speculation-space) would be a measure of the light generated in ratio to wasted heat - Of special significance for large high-current LEDs as used in lighting fixtures, where significant design effort goes into cooling / heat-sinking design for the LEDs. Higher the efficiency, lower would be the cooling cost per lumen of light. Where does one draw the border on this? The marketing folks would have to say.

In summary: Until global standardization of these terms, and compliance with such standards, this is essentially marketing-speak.