Shabdam is a Bharatanatyam Item in which the Expressions (or Abhinaya) are introduced for the first time in the repertoire. The song (saahityam) is usually separated into stanzas and between each stanza, you'll have a simple Korvai (nritta steps). Each stanza can contain a different story or all of them put together is one single story. But essentially the whole item is about one person, one theme.
Lines of lyrics and rhythmic syllables (jatis) alternate in shabdam. Thus both abhinaya as well as the nritta is found here. Shabda means words of praise, hence a shabdam is a piece in which the deity/God or the king are praised for their deeds, glory, generosity and qualities. In Sanskrit it is called Yashogita, a song in praise praising the subjects' fame.
The movements here are leisurely. In the Shabdam, emotions are withheld at the beginning; thereafter, when the dancer has clarified herself, they are released in a measured and disciplined manner.
Shabdams are also referred to as Yashogeethams . They have also inherited an Islamic Influence of repeating the Salaam or Namostute (paying respects to the Almighty or the King) at the end of each line. This pleased the patrons. Initially Shabdams were composed and rendered in one Raaga. But it is now a common practice to use one Raaga (or tune) for each stanza and present the composition in Raagamalika.