This is the 11747th most frequent French word.
slackline
Slackline: A sport or activity involving balancing and walking on a taut, flat webbing stretched between two anchor points.
In this sentence, "slackline" is used as a noun referring to the sports equipment—a stretchy line used for balancing and walking.
J'adore pratiquer la slackline au parc le week-end.
I love practicing slacklining at the park on weekends.
Here, "slackline" is again a noun but pertains to the act of walking across the suspended line.
Il faut être concentré pour réussir à traverser la slackline sans tomber.
You need to be focused to manage crossing the slackline without falling.
In this case, "slackline" is used as a noun to describe the equipment being set up for practice.