A bribe was a gift (often in the form of money) intended to gain favor with a person of influence. Most cultures considered bribery morally reprehensible, although in many cases (e.g. the Cardassian Union) it was widespread, despite its being frowned upon. The Ferengi Alliance was a notable exception; bribes were considered a normal part of day-to-day life, to the point that it was sometimes considered rude not to bribe someone.
Examples
In 2135, T'Pol bribed a Tellarite transport captain, who ferried two Vulcan fugitives – Jossen and Menos – aboard his ship to Risa, in order to determine the exact location of the former operatives. (ENT: "The Seventh")
In 2267, James T. Kirk from the mirror universe attempted to bribe Spock after being detained on board the USS Enterprise in the brig once he arrived there due to a transporter accident. The mirror Kirk offered Spock the chance to be a "rich man". (TOS: "Mirror, Mirror")
Worf considered Deanna Troi's suggestion of drawing up a family contract with his son Alexander Rozhenko to be "bribery," however Troi explained that the contract would outline responsibilities for the both Alexander and him. (TNG: "Cost Of Living")
The Cardassian military was rife with corruption. During the Occupation of Bajor, Quark was able to conduct illegal business at his bar, as he knew Gul Dukat could be bribed into looking the other way so long as it was nothing that would gain the attention of his superiors. Other officers like Boheeka were willing to do Quark a favor now and again if the price was right. Ranjen Winn Adami was also able to bribe Cardassian officers with gemstones for small acts of kindness. (DS9: "Necessary Evil", "The Wire", "'Til Death Do Us Part")
Nu'Daq attempted to bribe Data in 2369 to learn the results of a computer analysis before it was revealed to everyone. Data, however, bluntly called Nu'Daq out on it, who subsequently said to forget it. (TNG: "The Chase")
In 2371, Quark planned to offer the family of Kozak a bribe if they sought him out and found his fabricated explanation for Kozak's accidental death unsatisfactory. (DS9: "The House of Quark")
That same year in the mirror universe, Elim Garak bribed Terran slaves in an attempt to increase the amount of ore that they processed in Terok Nor's ore processing center. Doing so, along with torture and executing unproductive slaves, failed to increase production enough to meet quotas set by the Klingon-Cardassian Alliance. Intendant Kira Nerys suggested randomly executing workers instead. (DS9: "Through the Looking Glass")
Officials in the Ferengi Commerce Authority (FCA) routinely bribe their way to power. Liquidators make up for this by charging citizens for virtually everything, even knowledge of what crime one has been charged with. The line between bribery and standard business proceedings often becomes blurred, such as at the Tower of Commerce, where visitors must pay three slips of latinum for the use of a chair while they wait and one slip if they wish to stand. (DS9: "Family Business")
When Rom had second thoughts about marrying Leeta, he considered bribing her into signing the standard Ferengi Waiver of Property and Profit females must sign prior to a wedding; however, he failed to take into account that the waiver would bequeath all of her property to him, making the bribe rather pointless. (DS9: "Ferengi Love Songs")
Liquidator Brunt was discharged from the FCA only to bribe his way back into power and position himself to become acting Grand Nagus when Zek was briefly deposed. (DS9: "Profit and Lace")
Part of Grand Nagus Zek's reforms, once he wrested control back from Brunt, was to make all bribes tax-deductible. Quark was outraged to hear this news, because he had never thought he would hear the "T-word" on Ferenginar. (DS9: "The Dogs of War")
Starfleet officers are often considered immune to bribes due to their moral code, which strictly prohibits such illicit behavior. However, they have been known to succumb to greed on occasion, becoming involved with organizations such as the Orion Syndicate. (DS9: "Honor Among Thieves") Additionally, in 2374, Captain Benjamin Sisko made a bribe himself when Quark inadvertently became ensnared in his plot to draw the Romulan Empire into the Dominion War. In order to prevent Quark from pressing charges against Grathon Tolar, who had attacked him, Sisko agreed to several of Quark's demands, including replacement of his and Impela’s clothing, 5 bars of Latinum and getting station security to release several cargo containers that they had been holding due to Quark's not having the proper import license. (DS9: "In the Pale Moonlight")
In 2376, The Doctor had several daydreams when his programming was taken over by new algorithms he'd added to his holoprogram. One of these was that Neelix had baked him a cake, which The Doctor thanked the Talaxian for, adding that it wouldn't get him out of his checkup. (VOY: "Tinker Tenor Doctor Spy")
In 2399, after Central Station on Vashti refused to grant Jean-Luc Picard entry through the planetary defense system, Cristóbal Rios suggested that a "cash gift" might open the way. (PIC: "Absolute Candor")