- mIş kadar

When this gerundium suffix comes to  the verb stem , it gives the meaning of "as if"

Sınavdan iyi not alınca, sınıfı geçmiş kadar sevindi.

When he got good point from the exam, he was as much happy as [ if ] he passed the class.

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It was only a good point that he got from the exam, there are still more exams to pass but he felt so happy as if he passed the [whole year] class.

And gerund seems to be "isimfiil" in English grammar.

And here´s how gerundivum is described in Latin itself:

Gerundivum

Gerundivum est modus verbi Linguae Latinae, accurate adiectivus verbalis passivus cuius significatio est aliquod debere facere, e.g dolor vix (non) ferendus aut labores non fugiendi. Nomen amanda sonat ergo "quae amari debet".

It could be understood as "sıfatfiil" in Turkish not "zarffiil".

- mAk yerine

Verb stem + mAk yerine    =====> Instead of

Bana öğüt vermek yerine kendi sorunlarını çöz.

Solve your own problems  instead of advising me.

[Deal with your own problems instead of preaching me.]

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Konuşmak yerine biraz da insanları dinlemeyi dene.

Try to listen to people abit instead of talking.

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But their equivalents are often zarffiil in Turkish:

he sat not moving - kımıldamadan oturdu

they came running - koşarak geldiler

Mary, leaning from the window, watched him - Mary, pencereden uzanarak, (onu) izledi

That´s why gerund is not isimfiil but zarffiil in Turkish grammar.. 

By the way the greatest authorities of the Turkish grammar call gerundium as zarffiil

-Anda

Verb stem + Anda ====> When

This form is used in folk songs and colloquial language especially it is a typical  gerundium of Azerbaijani dialect.

Aklıma sen gelende gönlümde çiçekler açar. ---->  My heart blossoms when you come to my mind.

We see this form in a nice folk song from Kerkük region ; it is called "Çakmağı çak"

çırağda yağ tükendi
ne yaman vakit tükendi
ne sennen bu güzellik
ne mennen ah tükendi

çakmağı çak
çırağı yandırmamışam
yarim için potin aldım
tekini yolda salmışam

çırağı yandıraydım
yol üste konduraydım
yarim bize gelende
heybesin endireydim

çırağım şule verdi
kölgesin güle verdi
neylerim yar men sennen
tez meni dile verdi

damda çırağ yandırır
manin görür söndürür
özü keyf sefada
meni dertten öldürür

and "Ersen ve Kardaşlar " in 70´s composed this folk song as their first 45´s. Enjoy the song 

http://www.youtube.com/watch?v=LNJspekCYi8

Well,

I suggest you start with reading identifying verbals for example. If you insinst then we can further talk.

Let´s forget about what they (i.e the greatest authorities of the Turkish grammar) call gerendivum. We are trying to sort out what gerund means in English language (The title is in English, right?).

I´ll copy the gerund part from the given link below:

Gerunds

A gerund is a verb form ending in -ing that functions in a sentence as a noun. Although both the present participle and the gerund are formed by adding -ing to a verb, note that the participle does the job of an adjective while the gerund does the job of a noun. Compare the verbals in these two sentences:

The children, crying and exhausted, were guided out of the collapsed mine.
Crying will not get you anywhere.

Whereas the participle crying modifies the subject in the first sentence, the gerund Crying is the subject of the second sentence.

It is in English but it is not about English.

It is impossible to create a grammar terminology which applies to every language in the world. For instance, we talk about Swedish or German auxiliaries, even Turkish auxiliaries even though we very well know they have very little in common with English auxiliaries. Grammar consists of continuums rather than strictly bordered units.

I believe transporting grammar terminology from one language to another has done damage to our understanding. Anyway, this is the way linguists at all times have struggled their way to more accurate definitions.

For some reason some grammarians have begun to use the term gerund in Turkish grammar denoting to the diverse group of adverb-like verb forms. And not only in Turkish as we saw in the Russian examples. I must admit I can’t quite understand why this happened. Probably for practical reasons. Practical reasons are as good as any. Words are agreements after all.

I think when you say "gerund" in English, you must stick to what it means in English, right?

I repeat: what they call "gerund" in English is called "isimfiil" in Turkish. That´s my understanding.

No.

So how do you define "gerund" in English? I have provided definitions and examples so far.

I would like to hear what definition you stick to.