In Lesson 1 we looked at cmene, Lojban names. cmene are typically understood to label one particular thing. Just as in English, if I say Mary, I mean one particular person called Mary at a time, no matter how many people there are in the world called Mary; so in Lojban, meris. can only refer to one person. This means that cmene normally do not stand for classes of things (like person, dog or computer) or for relationships between things (like loves, gives or is inside).
Note: Those of you already advanced in Lojban wisdom will point out that mass names don't name 'one particular thing'. True; but if you know that much Lojban, you also know what the real distinction between a predicate and a name is anyway, so you know where this simplification is coming from. The rest of you, er, carry on.
Relationships are the key to Lojban, and words describing a relationship are said to act as selbri. A selbri is not a type of word (like a 'verb' in English); it is something that some types of words can do. Various types of word can act as selbri, but cmene, as we've seen, cannot.
The main type of word used as a selbri is a gismu, or root-word. These are the building blocks of Lojban vocabulary. gismu are easy to recognise, because they always have five letters, in the form
CVCCV — e.g. gismu, dunda, sumti
CCVCV — e.g. cmene, bridi, klama