A judgment may run a hundred pages, but only part of it is law. The ratio decidendi — the legal rule necessary to the actual decision on the facts — is what binds later courts. Observations along the way — how a different case might be decided, doubts about another doctrine — are obiter dicta: said in passing, entitled to respect, but not binding.
Separating ratio from obiter is a core lawyerly skill and a genuinely contested art. Courts wanting room to move read an awkward precedent's ratio narrowly ('distinguishing' it on its facts); courts wanting to consolidate the law read it broadly.
The Supreme Court of Canada has cautioned against a mechanical ratio/obiter line, holding that considered statements in its judgments — even beyond the strict ratio — should generally be followed by lower courts.