Lambdamoo Programmer's Manual passage:
"The `r' bit controls whether or not players other than the owner of this object can obtain a list of the properties or verbs in the object."
The bits are set with a chmod command:
@chmod #thing +r
sets r bit on, @chmod #thing -r
sets r bit offAll items are created readable by default. In addition, #thing.property and #thing:verb can also be @chmod'ed, for instance if you wanted to make a specific verb or property non readable on something you made.
Good news: You never have to worry about this flag because don't make your shit unreadable 8) More often you'll be doing
@chmod #somethingimade +f
which allows something to be spawned into the world. Another common command will be @chmod #somethingimade.someproperty -c
in order to give other programmers permission to change properties you have defined when they create a child of that object.