Cannabis distillate, also known as CO2 oil and hash oil, is an edible, smokable product made by extracting the natural oil found in dried cannabis flowers and refining it in laboratory conditions until it contains—mostly—only one specific cannabinoid, commonly THC or CBD, though "full spectrum" distillate, containing 50/50% THC/CBD and other combinations using both, are also available in areas where cannabis consumption is legal.
Distillate itself is a golden, thickly viscous, transparent liquid. To the touch, it is sticky, and to the taste, it is sour, although this is not apparent when using distillate to infuse food for making cannabis edibles. Smoked, the taste is highly variable based on a number of factors: the strain of cannabis (e.g., OG Kush, Jack Herer, Durban Poison, etc) used in the preparation, the age of the liquid (the newer, the fresher, generally), storage conditions (keep it in an airtight container, away from bright light and high humidity for prolonged periods) and the varied use of cannabis-derived terpenes during preparation.
Because distillate is concentrated, it contains a much higher amount of THC (or CBD) than raw flower could ever produce—while most flower averages 12-18% and tops out at 25-30% THC, distillate is engineered to commonly contain 60-95% THC.
Distillate commonly comes in pre-filled cartridges and is consumed with a vaporizer (aka "battery"). Engaging the vaporizer causes a tiny amount of distillate from the cartridge to evaporate and the THC present in the oil is carboxylated into THCA vapor, with the vapor inhaled through the cartridge via its mouthpiece into the lungs. Here's a brief demonstration of using a vaporizor pen, one of the more common forms of batteries used for consuming distillate. Here's a more thorough explanation.
Smoking distillate doesn't require nearly as much effort or energy as smoking flower does. It's very different than smoking flower. The vapor is quite unlike smoke; though it has the same consistency, it's thinner and easier to inhale, and less likely to induce coughing. The exhaled clouds of vapor are much less voluminous than those produced by combustion-generated smoke, and the vapor dissipates within moments and doesn't accumulate. Perhaps best of all, it leaves no smell whatsoever on fabric, skin or breath, and it doesn't leave sticky resin on the surfaces of oft-smoked-in rooms. Unlike smoke, which is made up of particulate matter, vapor is liquid-based, leading to a much cleaner experience. It's so discreet that it may be used in almost any situation for immediate relief if you can get a moment's privacy.
The effects, of course, vary intensely from person to person, but for me, it's something like what "marijuana-lite" might mean. I can still function when vaping, unlike with flower where I'd often get to a point where normal function was a little difficult, and it's very effective at relieving my pain specifically (which is caused by Crohn's disease) and even better at abating my intense, often paralyzing anxiety. I like to vape for an hour or two before bed every night so the anxiety and recurring severe pain don't keep me awake. Others prefer to vape lightly throughout the day for a more even and measured response to chronic pain and anxiety along with a host of other issues such as epileptic seizures.
There are a great many different brands of cannabis distillate vape cartridges ("carts" for 510-thread screw-on cartridges, "pods" for Juul-style magnetic drop-in tanks) available in jurisdictions where the sale of such products is legal. At the time of this writing, several countries and a majority of American states allow the retail sale of cannabis products in various forms. Living in Michigan, as I do, where medical cannabis has been legal since 2008 and recreational since 2018, some of my preferred brands include Platinum Vape, Select and STiiiZY. These are available in most of the dispensaries I've visited or had delivery from over the years that I've had a medical marijuana card (2014-present), which entitles me to cheaper prices on cannabis products in my state of residence, compared to the sale of recreational cannabis products that often sell for triple the price. It's important to make sure that the cartridge you buy is genuine, as fake cartridges proliferate even in legal markets where they have no need to, frequently to get around safety testing requirements imposed by local governments. There's a particular subreddit just for that purpose: identifying fakes. As ever with this sort of thing, use caution.
What is Distillate? Cannabis Distillate Definition by Weedmaps
What is Cannabis Oil Distillate and How is it Made?
Reddit - Legal Oil Cart Discussion
Wikipedia: Hash oil, which covers the subject, but should really be split it into a separate article for the solvent-derived/hydrocarbon extracts section, which is what this writeup refers to.