Forgive - Mark 11:25 & Mt 6:14

 Mrk 11:25  And G2532  when G3752  ye stand G4739  praying, G4336  forgive, G863  if G1487  ye have G2192  ought G5100  against G2596  any: G5100  that G2443  your G5216  Father G3962  also G2532  which G3588  is in G1722  heaven G3772  may forgive G863  you G5213  your G5216  trespasses. G3900 

Forgive: G863   (Strong)

ἀφίημι

aphiēmi

af-ee'-ay-mee

From G575 and ἵημι hiēmi (to send; an intensive form of εἶμι eimi (to go)); to send forth, in various applications: - cry, forgive, forsake, lay aside, leave, let (alone, be, go, have), omit, put (send) away, remit, suffer, yield up.

Trespass: G3900   (Strong)

παράπτωμα

paraptōma

par-ap'-to-mah

From G3895; a side slip (lapse or deviation), that is, (unintentional) error or (wilful) transgression: - fall, fault, offence, sin, trespass.

Mat 6:14  For G1063  if G1437  ye forgive G863  men G444  their G846  trespasses, G3900  your G5216  heavenly G3770  Father G3962  will also G2532  forgive G863  you: G5213 

Forgive: G863   (Strong) aphiēmi

Trespass: G3900   (Strong) paraptōma

My conclusion: 

The two verses have the same meanings on "forgive" and "trespass." 

Albert Barnes' Commentary on Matthew 6:14-15

For if ye forgive men their trespasses - If ye forgive others when they offend or injure you.

Your heavenly Father will also forgive you - This is constantly required in the Bible. See the notes at Mat 6:12. Our Saviour says we should forgive even if the offence be committed seventy times seven times, Mat 18:22. 

By this is meant, that when a man asks forgiveness, we are cordially and forever to pardon the offence; we are to declare our willingness to forgive him.

If he does not ask forgiveness, yet we are still to treat him kindly; not to harbor malice, not to speak ill of him, to be ready to do him good, and be always prepared to declare him forgiven when he asks it, and if we are not ready and willing to forgive him; we are assured that God will not forgive us.

Appendix: 

Albert Barnes' Commentary on Mat 6:12

Mat 6:12  And G2532  forgive G863  us G2254  our G2257  debts, G3783  as G5613  we G2249  forgive G863  our G2257  debtors. G3781 

Forgive: G863   (Strong) aphiēmi

Debts: G3783   (Strong)

ὀφείλημα

opheilēma

of-i'-lay-mah

From (the alternate of) G3784; something owed, that is, (figuratively) a due.; morally a fault: - debt.

And forgive us our debts ... - The word “debts” is used here figuratively.

It does not mean “literally” that we are “debtors to God,” but that our sins have a resemblance to debts. Debtors are those who are bound to others for some claim in commercial transactions; for something which we have had, and for which we are bound to pay according to contract. “Literally” there can be no such transaction between God and us. It must be used figuratively. We have not met the claims of law. We have violated its obligations. We are exposed to its penalty. We are guilty, and God only can forgive, in the same way as none but a “creditor” can forgive a debtor.

The word “debts” here, therefore, means “sins,” or offences against God - offences which none but God can forgive. In the parallel place in Luk 11:4, the word sins is used. The measure by which we may expect forgiveness is that which we use in reference to others See Psa 18:25-26; Mat 18:23; Mrk 11:26; Luk 11:4.

This is the invariable rule by which God dispenses pardon He that comes before him unwilling to forgive, harboring dark and revengeful thoughts, how can he expect that God will show him that mercy which he is unwilling to show to others? It is not, however, required that we should forgive “debts” in a pecuniary sense. 

To them we have a right, though they should not be pushed with an overbearing and oppressive spirit; not so as to sacrifice the feelings of mercy in order to secure the claims of justice. No one has a right to oppress; and when a debt cannot be paid, or when it would greatly distress a debtor’s wife and children, or a widow and an orphan, or when calamity has put it out of the power of an honest man to pay the debt, the spirit of Christianity requires that it should be forgiven. 

To such cases this petition in the Lord’s prayer doubtless extends. But it was probably intended to refer principally to injuries of character or person which we have received from others. If we cannot from the heart forgive them, we have the assurance that God will never forgive us.