Also found in: Dictionary, Thesaurus, Medical, Legal, Financial, Encyclopedia.
1. verb To move backwards. This phrase is commonly used to refer to maneuvering a car in reverse. Back up, you're standing too close to me! If you back up a little, then your car will be completely in that parking space.
2. verb To save copies of computer files in another place, in case the original files become inaccessible. If you didn't back up your files before the computer crashed, they may be lost forever.
3. verb To become clogged and impassable. I'm calling the plumber right now because the toilet is backed up again. Traffic is totally backed up, due to all that construction.
4. verb To return to an item previously mentioned. Whoa, back up—Janet and Jim are getting married?
5. verb To support or assist someone. In this usage, a noun or pronoun can be used between "back" and "up." You didn't see that meeting on the calendar, either? OK, please back me up on this, so the boss doesn't think I'm an idiot.
6. noun An alternate to be used if it becomes necessary for some reason, typically the failure, ineffectiveness, or the absence of the original. The phrase is typically written as one word. I brought an extra pen as a backup, in case this one runs out of ink during the exam. I hope Tony asks me to the prom, but, if not, I have my best friend Bill as a backup.
7. adjective Available for use as an alternate if it becomes necessary for some reason, typically the failure, ineffectiveness, or the absence of the original. The phrase is typically written as one word. I brought three backup pens, in case this one runs out of ink during the exam. I'm the backup quarterback, but I still have to know all the plays in case I get in the game. I hope Tony asks me to the prom, but, if not, I have my best friend Bill as a backup date.
8. adjective Appearing in the background in support of a main act or performer. The phrase is typically written as one word. She's auditioning backup dancers for her world tour today.
back someone up
to provide someone with help in reserve; to support someone. Don't worry. I will back you up when you need me. Will you please back up Nancy over the weekend?
back something up
1. Lit. to drive a car backwards. Will you back your car up a little? I will back up the car.
2. Lit. to cause objects to obstruct a pathway or channel and cause a slowdown in the flow. The wreck backed the cars up for a long way. Some dead branches and leaves backed the sewer up.
3. Fig. to give additional support or evidence about something. (To support or strengthen the facts.) My story of the crime will back your story up. That backs up my story, all right.
back up (to something)
to go back to something said in a conversation. Wait—back up a little. What did you say that phone number was? Let's back up to what you just said and go over that point again.
1. Lit. [for objects] to obstruct and accumulate in a pathway or channel. Something clogged the sewer and it backed up.
2. Fig. to refuse to go through with something; to back out (of something). Fred backed up at the last minute, leaving me to do the job alone.
1. Move or drive a vehicle backward, as in He told her to back up into the garage. [First half of 1800s]
2. Bring or come to a standstill, as in The water had backed up in the drains, or The accident had backed up traffic for miles. [First half of 1800s]
3. Support or strengthen, as in The photos were backed up with heavy cardboard so they couldn't be bent, or I'll back up that statement of yours. [Second half of 1700s]
4. Duplicate a file or program so that the original is not lost. For example, Every computer manual warns you to back up your work frequently in case of a power outage or computer failure . [Second half of 1900s]
1. To move backward: We passed the house we were looking for, so we had to back up a little bit.
2. To move something or someone backward: I backed the car up against the garage wall. Let's back up the car to the curb.
3. To prove something to be true: There was not enough evidence to back up the theory. What I told you is true, and now I have even more evidence to back it up.
4. To support someone by confirming that they are telling the truth: We told our version of the events, certain that the witnesses would back us up. They won't back up anyone who is known for lying.
5. To provide help or support for someone or something: If I decide to take on the job, can I count on you to back me up? The political party backs up any candidate who follows its basic principles.
6. To cause to accumulate, especially due to an obstruction: The accident backed the traffic up for blocks. Something got stuck in the drain, and now the kitchen sink is backed up.
7. To make a copy of a computer program or file for use if the original is lost or damaged: I backed up the disk so that I wouldn't lose any data. Be sure to back your files up before you turn off the computer.
in. to refuse to go through with something; to back out (of something). Fred backed up at the last minute, leaving me with twenty pounds of hot dogs.
mod. drug intoxicated. Old Benny’s really backed up.