What Happens If U.S. Supreme Court Decisions End In A Tie?

The Supreme Court bench has nine seats, but now with a vacant seat, there's room for a tie. So what happens if court's vote ends in a tie?

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Major Supreme Court Cases in 2015 (nytimes.com)
"Lethal Injection: The court decided in Glossip v. Gross that states may use a drug linked to apparently botched executions to carry out death sentences."

The Supreme Court of the United States (fjc.gov)
"The Supreme Court of the United States is the highest court in the nation. "

Supreme Court Justices' Recusal Decisions Should be Transparent and Reviewable (afj.org)
"It is a basic precept that no one should be a judge in his or her own case."

Court's Tie Vote Sustains Swatch Against Costco (nytimes.com)
"The Supreme Court said Monday that it deadlocked, 4-4, and would not decide a copyright infringement case involving the discount warehouse chain Costco Wholesale over the resale of imported Swiss watches made by a Swatch Group unit."