Marcato is Italian for marked, meaning the notes are to be accented and emphasized. In tango the notes are also played clipped or cut shorter than the note value as written. That is called staccato. The performance style, the , combines marcato and staccato. And that gives the music a crisp and bold character. When I use the term marcato those are the qualities I mean.
Tango uses marcato style playing very often, in both the melody and especially the accompaniment, frequently played by the bandoneons, but others as well.
The way the notes are played and connected to one another: anywhere from gently played to heavily attacked; held for the full duration of the note value or clipped short; smoothly connected to the notes before and after, or continuously separated.
There are many technical terms for these differences, but for tango we mostly need to be aware of two broad kinds of articulation, the extreme ends of the spectrum: a connected legato, which often creates a lyrical quality, and an accented, clipped short marcato. Generally, the strings and singers have a legato articulation, while the bandoneons have a marcato one.