What does 'let dry lightly between waterings' mean?

[greenochre]

Hi, I recently got two new orchids - Isabelia pulchella and Epidendrum parkinsonianum, and care tips about both says they should be 'let dry lightly' between waterings.

Honestly, I don't get what's 'dry lightly' means.
I understand that it's somewhere in between Bulbophyllum (always moist substrate) and Phalaenopsis or Dendrobium (let the substrate dry completely before watering again), but where exactly? And how would I know that I got the right wetness?

Isabelia is mounted with some sphagnum and I put it near Aerangis Modesta, also mounted, very close to humidifier - basically, the most humid corner of my plant shelf. (humidity is 80-90%). Epidendrum I repotted from the pot to hanging net basket with sphagnum/perlite/lava rock mix