Backlinks are also called inbound or incoming links. Quality matters far more than quantity: one relevant link from a respected site usually beats dozens from low-quality pages.
Search engines look at the linking page's authority, its topic, the anchor text, and whether the link is dofollow.
Why it matters when you launch
A launch is one of the few moments when many sites will link to a new product at once. Directory listings, launch platforms, newsletters, and press give you your first backlinks.