The basics: A retrograde occurs when a planet appears to be moving backwards from our vantage point here on Earth. It isn't actually moving backwards, it just appears that way. Mars retrogrades every two years or so, and the retrograde lasts for 2-3 months. When a planet retrogrades, what that planet rules tends to be thrown off, along with what the sign it's retrograding in rules.
And the retrograde train continues! We end the Mercury retrograde on February 28th, and the very next day, Mars turns retrograde. Before that, we had Venus retrograde starting in mid-December, and after this Mars retrograde, we'll have another Mercury retrograde, so we don't get a break until July. We're in the middle of it now people, so let's try to stay calm and power through!
Mars is the planet of drive and energy, and when he retrogrades, we usually lack this. We're lazier, we don't want to start anything new or even get up off of the couch, and our tempers flare when anyone tries to point out what we're doing is wrong. For this retrograde, Mars will be entirely in the sign of Libra.
Libra rules committed relationships, so we'll lack drive and energy most with our relationships and with those we're closest to. We'll likely see the ending of many relationships during this retrograde, and couples will seem to fight a lot more than usual. When people break up, it could be sudden and messy.
Conversely, we could see some couples get back together, since a retrograde is a time of redoing. That doesn't necessarily mean that these couples will stay together though. We could also see some couple from the past become important for some reason, find their way back into the spotlight, and demand our attention.
Mars is Libra is usually concerned with justice and fairness, so Mars retrograde here could make us not want to do anything about making sure we have true justice and that everyone's being treated fairly. It could also make us more angry when we see injustice and unfairness, but we just get rageful instead of really productive.
Mars is Libra likes compromise, and we'll probably want to the opposite of that now. We want to win at all costs, and it's to our detriment. We don't care about trying to find the best outcome possible for all parties involved, and we sure as hell don't care about keeping the peace. We want a fight, and we'll get it.
The turn retrograde will be square (hard aspect) Venus in earth sign Capricorn. We could have a surge of passion that we can't let out properly and it drives us to do mad things, or lack the passion we're looking for and are desperate for some inspiration. This aspect is exact on March 2nd, the day after Mars turns retrograde.
The trouble aspects for this Mars retrograde are when Mars opposes the Sun on April 8th (short fuses, aggression), opposes Mercury on April 16th (fights), squares Jupiter April 22nd (too full of ourselves), opposes Uranus and squares Pluto on April 23rd (too brash and impulsive, violent anger), and opposes Venus on May 11th (out of control passion).
One of the main issues with this retrograde is that we'll experience a t-square (or t-cross) during the month of March with Jupiter ending its retrograde in Cancer on March 6th, and it's square Uranus in Aries and opposite Pluto in Capricorn, so all cardinal signs.
The missing sign is Libra, which is the sign Mars is retrograding in, but he's quite far away in Libra from the other 3 planets, which are earlier in their signs. This can be felt through May, and it's a little concerning since when this occurred last year, we had the Syria debacle. Hopefully, it passes by without anything so serious happening this time.
The turn retrograde begins at 27 degrees Libra, so those of you Libras born October 19th - 22nd may feel the turn retrograde most. The turn direct occurs at 9 degrees Libra, so those of you Libras born October 1st - 4th may feel the turn direct most. All Libras born October 1st - 22nd will feel the impact of Mars on their Sun at some point during this retrograde.
For the rest of you, check the house(s) Mars will be retrograding in of your own natal chart, and any aspects Mars will make during its retrograde to your natal planets, to fully understand how it will impact you personally.
If you have Mars retrograde in your natal or progressed chart, you may not feel the worst of this. Those individuals generally don't experience the difficulties of the retrograde because it feels more natural to them. Of course, chances are everyone else around them doesn't have the same aspect, so they can still experience difficulties brought on by others.
Suggested Reading: The Mercury, Venus and Mars Retrogrades page for general interpretations